EPA/530/SW-91/051
May 1991
TECHNICAL GUIDANCE DOCUMENT:
INSPECTION TECHNIQUES FOR THE FABRICATION
OF
GEOMEMBRANE FIELD SEAMS
Cooperative Agreement No. CR-815692
Project Officers
Robert E. Landreth
David A. Carson
Waste Minimization, Destruction & Disposal Research Division
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
Office of Solid Waste and Emergency Response
U.S. Enironmental Protection Agency
Washington, D.C.
In cooperation with
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
Printed on Recycled Paper
-------
DISCLAIMER
The preparation of this document has been funded wholly by the United
States Environmental Protection Agency. It has been subjected to the
Agency's peer and administrative review, and it has been approved for
publication as an EPA document. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
ii
-------
FOREWORD
Today's rapidly developing and changing technologies and industrial
products and practices frequently carry with them the increased generation of
solid and hazardous wastes. The U.S. Environmental Protection Agency is
charged by Congress with protecting the Nation's land, air, and water
resources. Under a mandate of national environmental laws, the agency strives
to formulate and implement actions leading to a compatible balance between
human activities and the ability of natural systems to support and nurture
life. These laws direct the EPA to perform research to define our
environmental problems, measure the impacts, and search for solutions.
The Risk Reduction Engineering Laboratory is responsible for planning,
implementing, and managing research, development, and demonstration programs
to provide an authoritative, defensible engineering basis in support of the
policies, programs, and regulations of the EPA with respect to drinking water,
wastewater, pesticides, toxic substances, solid and hazardous wastes, and
Superfund-related activities. This publication is one of the products of that
research and provides a vital communication link between the research and the
user community.
This document provides guidance for construction quality control and
construction quality assurance inspectors and related personnel as to the
proper techniques for fabricating field seams in geomembranes. It focuses on
six technical areas used to fabricate field seams of all types of
geomembranes. The presentation of this information details geomembrane
material preparation, equipment preparation, seam method evaluation through
test strips, seaming process, inspection activities after seaming, and
instructions for seaming under unusual conditions. Rationale is provided for
the various conditions and limitations that are suggested. A glossary of
terms relevant to the field seaming of geomembranes is provided at the end of
the document.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
iii
-------
PREFACE
Subtitle C of the Resource Conservation and Recovery Act (RCRA) requires
the U.S. Environmental Protection Agency (EPA) to establish a Federal
hazardous waste management program. This program must ensure that hazardous
wastes are handled safely from generation until final disposition. EPA issued
a series of hazardous waste regulations under Subtitle C of RCRA that are
published in Title 40 Code of Federal Regulations (40 CFR). The principal 40
CFR Part 264 and 265 regulations were issued on July 26, 1982 for treatment,
storage, and disposal (TSD) facilities and establish performance standards for
hazardous waste landfills, surface impoundments, land treatment units, and
waste piles. The regulations have been amended several times since then.
In support of the regulations, EPA has been developing three types of
documents to assist preparers and reviewers of RCRA permit applications for
hazardous waste TSO facilities. These include RCRA Technical Guidance
Documents, Permit Guidance Manuals, and Technical Resource Documents (TRDs).
RCRA Technical Guidance Documents, such as this one, present design and
operating parameters or design evaluation techniques that generally comply
with, or demonstrate compliance with, the Design and Operating Requirements
and the Closure and Post-Closure Requirements of 40 CFR Part 264.
The Technical Resource Documents present summaries of state-of-the-art
technologies and evaluation techniques determined by the Agency to constitute
good engineering designs, practices, and procedures. They support the RCRA
Technical Guidance Documents and Permit Guidance Manuals in certain areas
(i.e., liners, leachate management, final covers, and water balance) by
describing current technologies and methods for designing hazardous waste
facilities, or for evaluating the performance of a facility design. Although
emphasis is given to hazardous waste facilities, the information presented in
these TRDs may be used for designing and operating nonhazardous waste TSD
facilities as well. Whereas the RCRA Technical Guidance Documents and Permit
Guidance Manuals are directly related to the regulations, the information in
these TRDs covers a broader perspective and should not be used to interpret
the requirements of the regulations.
This document is a Technical Guidance Document prepared by the Risk
Reduction Engineering Laboratory of EPA's Office of Research and Development
in cooperation with the Office of Solid Waste and Emergency Response. The
document has undergone extensive technical review and has been revised
accordingly. With the issuance of this document, all previous drafts are
obsolete and should be discarded.
iv
-------
Comments are welcome at any time on the accuracy and usefulness of the
information in this document. Comments will be evaluated, and suggestions
will be incorporated, wherever feasible, before publication of any future
revisions. Written comments should be addressed to EPA RCRA Docket (OS-305),
401 M Street S.W., Washington, DC 20460. The document for which comments are
being provided should be identified by title and number.
-------
ABSTRACT
This Technical Guidance Document Is meant to augment the numerous
construction quality control and construction quality assurance (CQC and CQA)
guidelines that are presently available for geomembrane installation and
inspection. It is focused on all current methods of producing geomembrane
seams including HOPE and VLDPE, PVC, PVC-R, CSPE, CSPE-R, CPE, CPE-R, EIA and
EIA-R. In general, the tone of most of the existing guidelines is to allow
the installer almost complete freedom in making seams with the only
conditions being that they pass;
(a) destructive shear and peel tests to a stipulated strength, and
(b) selected nondestructive tests.
By developing a report somewhere between the typical CQC/CQA Documents
and an installer's training manual, i.e., a "Technical Guidance Document", it
is hoped that this document will provide meaningful insight for an inspector
as to what the installer is trying to accomplish. At the same time it might
be also helpful to the installer in recognizing that others have an interest
in their specific activity. After some introductory material, the manual
presents six specific methods used for fabricating field seams of the types
of geomembranes being most widely used for environmental control systems.
They are the following:
extrusion fillet seams
extrusion flat seams
hot wedge seams
hot air seams
chemical fusion seams
adhesive seams
VI
-------
TABLE OF CONTENTS
PAGE
DISCLAIMER ii
FOREWORD iii
PREFACE iv
ABSTRACT vi
LIST OF FIGURES x
LIST OF TABLES xv
ACKNOWLEDGEMENTS xvi
SECTION 1. INTRODUCTION AND AUDIENCE 1
SECTION 2. CONSTRUCTION QUALITY ASSURANCE CONCEPTS 5
SECTION 3. TERMINOLOGY AND PREPARATORY ISSUES 9
3.1 TERMINOLOGY 9
3.2 PREPARATORY ISSUES 11
3.3 UNITS 13
3.4 TEST STRIPS 14
SECTION 4. AN OVERVIEW OF FIELD SEAMING METHODS 19
SECTION 5. DETAILS OF EXTRUSION FILLET SEAMS 23
5.1 GEOMEMBRANE PREPARATION 23
5.2 EQUIPMENT PREPARATION 26
5.3 TEST STRIPS 29
5.4 ACTUAL SEAMING PROCESS 31
5.5 AFTER SEAMING 40
5.6 UNUSUAL CONDITIONS 41
SECTION 6. DETAILS OF EXTRUSION FLAT SEAMS 45
6.1 GEOMEMBRANE PREPARATION 45
6.2 EQUIPMENT PREPARATION 48
6.3 TEST STRIPS 49
6.4 ACTUAL SEAMING PROCESS 54
6.5 AFTER SEAMING 57
6.6 UNUSUAL CONDITIONS 58
vii
-------
TABLE OF CONTENTS (continued)
PAGE
SECTION 7. DETAILS OF HOT WEDGE SEAMS 63
7.1 GEOMEMBRANE PREPARATION 63
7.2 EQUIPMENT PREPARATION 66
7.3 TEST STRIPS 71
7.4 ACTUAL SEAMING PROCESS 73
7.5 AFTER SEAMING 78
7.6 UNUSUAL CONDITIONS 80
SECTION 8. DETAILS OF HOT AIR SEAMS 85
8.1 GEOMEMBRANE PREPARATION 85
8.2 EQUIPMENT PREPARATION 91
8.3 TEST STRIPS 95
8.4 ACTUAL SEAMING PROCESS FOR THE MANUAL, HAND-HELD TYPE
OF HOT AIR SEAMING 97
8.5 ACTUAL SEAMING PROCESS FOR THE AUTOMATED, MACHINE-DRIVEN
TYPE OF HOT AIR SEAMING 101
8.6 AFTER SEAMING 103
8.7 UNUSUAL CONDITIONS 105
SECTION 9. DETAILS OF CHEMICAL AND BODIED CHEMICALLY FUSED SEAMS .... 109
9.1 GEOMEMBRANE PREPARATION 109
9.2 EQUIPMENT PREPARATION 114
9.3 TEST STRIPS 116
9.4 ACTUAL SEAMING PROCESS 121
9.5 AFTER SEAMING 126
9.6 UNUSUAL CONDITIONS 128
SECTION 10. DETAILS OF CHEMICAL ADHESIVE SEAMS 132
10.1 GEOMEMBRANE PREPARATION 132
10.2 EQUIPMENT PREPARATION 137
10.3 TEST STRIPS 139
10.4 ACTUAL SEAMING PROCESS 144
10.5 AFTER SEAMING 149
10.6 UNUSUAL CONDITIONS 152
viii
-------
TABLE OF CONTENTS (concluded)
PAGE
SECTION 11. EMERGING TECHNOLOGIES FOR GEOMEMBRANE SEAMING 156
11.1 ULTRASONIC SEAMS 156
11.2 ELECTRICAL CONDUCTION SEAMS 158
11.3 MAGNETIC INDUCTION SEAMS 158
SECTION 12. REFERENCES 162
SECTION 13. GLOSSARY OF TERMS 166
ix
-------
LIST OF FIGURES
FIG. NO. PAGE
3.1 Test strip process flow chart 16
5.1 Type of hook blade used for the cutting of liner materials 24
5.2 Hand-held electric rotary grinder with circular disc grit
grinding paper 27
5.3 Photographs of various types of extrusion fillet welding
devices 28
5.4 Test strip process flow chart 30
5.5 Fabrication of geomembrane seam test strip 32
5.6 Preparing the bevel of the upper geomembrane for liner
thicknesses greater than 1.5 mil 34
5.7 Proper orientation and grinding preparation of sheets prior
to tacking and extrudate placement 35
5.8 Photographs of different orientations of grinding patterns 36
5.9 Photographs of different extent of grinding patterns after
extrusion fillet seaming 38
5.10 Smooth propping wedge used when tacking of sheets is done
before surface grinding of geomembrane sheets 39
5.11 Schematic diagrams of various cross sections of extrusion
seams 39
5.12 Photographs of cross sections of various types of HOPE
extrusion fillet seams 42
6.1 Type of hook blade used in the cutting of liner materials 47
6.2 Grinding locations and method used in the preparation of
extrusion flat seams 49
6.3 Test strip process flow chart 51
-------
LIST OF FIGURES (continued)
FIG. NO. PAGE
6.4 Fabrication of geomembrane seam test strip 52
6.5 Photographs and schematic diagram of extrusion flat seaming
of geomembrane sheets 56
6.6 Schematic diagram of cross section of extrusion flat seam
with extrudate out to the edge of the upper geomembrane 57
6.7 Photographs of cross sections of HOPE extrusion flat seams 59
7.1 Type of hook blade used in the cutting of liner materials 65
7.2 Various types of hot wedge seaming devices 68
7.3 Diagrams of the hot wedge elements upon which the two sheets
to be joined are passed 69
7.4 Test strip process flow chart 72
7.5 Fabrication of geomembrane seam test strip 74
7.6 Details of the hot wedge system showing relative positions of
the hot wedge, rollers and sheets to be joined 76
7.7 Hot wedge T-seam detail 79
7.8 Schematic diagram of cross section of dual (split) hot wedge
seam illustrating squeeze-out 80
7.9 Photographs of cross sections of HOPE hot wedge seams 81
8.1 Trimming of excess geomembrane to obtain proper overlap prior
to seaming 87
8.2 Type of scissors recommended for cutting geomembranes 87
8.3 Photographs of "fishmouth" and its correction and patching .... 88
8.4 Various types of hot air seaming devices 92
8.5 Cross section of automated machine-driven hot air seaming
device for geomembranes 94
8.6 Test strip process flow chart 96
xi
-------
LIST OF FIGURES (continued)
FIG. NO. PAGE
8.7 Fabrication of geomembrane seam test strip 98
8.8 Fabrication of a field seam using manual hand-held hot air
seaming technique 100
8.9 Fabrication of a field seam using automated, machine-driven
hot air seaming technique 102
8.10 Dual track hot air machine T-seam detail for HOPE or VLDPE 104
8.11 Schematic diagrams of cross sections of single and dual
hot air seams illustrating squeeze-out 105
8.12 Cross sections of EIA liner seams fabricated by the hot air
method showing left, center, and right sides of completed
seam 106
9.1 Trimming of excess geomembrane to obtain proper overlap prior to
seaming Ill
9.2 Photographs of a "fishmouth" and its correction and patching. . . .112
9.3 Photograph of squirt bottles and method of application 115
9.4 Photograph of types of rollers used to apply pressure to
chemically bonded seams 116
9.5 Test strip process flow chart 118
9.6 Photographs of preparation of a field test strip prior to
production seaming 119
9.7 Positioning of wooden "seaming board" beneath seam area of
liner to provide for a uniform and smooth subsurface 122
9.8 Perspective diagram of locations where "T" configurations
commonly occur 123
9.9 Photograph of "T" trimming tool shaving the upper surface
of an existing seam in preparation of new intersecting seam . . . .123
9.10 Application of fusion chemical 125
xii
-------
LIST OF FIGURES (continued)
FIG. NO. PAGE
9.11 Initial rolling motion parallel to seam for the fabrication
of chemically fused seams of PVC liners 125
9.12 Photographs of air lance and pick testing of completed seam . . . .127
9.13 Cross sections of PVC liner seams fabricated by the chemical
fusion seaming method showing left, center, and right sides
of completed seam 129
10.1 Trimming of excess geomembrane to obtain proper overlap prior
to seaming and types of scissors recommended for cutting of
geomembranes 134
10.2 Photographs of a "fishmouth" and its correction and patching . . .135
10.3 Photograph of types of rollers used to apply pressure to
bodied fusion chemical seams 138
10.4 Test strip process flowchart 141
10.5 Photographs of preparation of a field test strip prior to
production seaming 142
10.6 Positioning of wooden seaming board beneath seam area 145
10.7 Perspective diagram of locations where "T" configurations
commonly occur 147
10.8 Photograph of "T" trimming tool shaving the upper surface of an
existing seam in preparation of new intersecting seam 147
10.9 Initial rolling motion parallel to seam for the fabrication
of adhesive seams for CEP, CSPE or PVC liners 148
10.10 Photographs of air lance and pick testing of completed seam . . . .150
10.11 Cross section of CSPE-R liner seams fabricated by the
chemical adhesive seaming method 151
11.1 Schematic diagrams of ultrasonic welding of plastic
(and metal) sheets 157
XI11
-------
LIST OF FIGURES (concluded)
FIG. NO. PAGE
11.2 Schematic diagram of rollers, ultrasonic horn and geomembrane
sheets in the ultrasonic seaming process 157
11.3 Schematic diagram of an electrofusion pipe coupling
process 159
11.4 Schematic diagram of the electrical conduction method of
joining geomembrane 159
11.5 Schematic diagram of the magnetic induction method of
joining geomembranes 160
xiv
-------
LIST OF TABLES
TABLE NUMBER PAGE
3.1 Polyethylene Types 10
3.2 Compounded Thermoplastics and Thermoplastic Elastomers 10
4.1 Fundamental Methods of Joining Polymeric Geomembranes 18
4.2 Most Commonly Used Field Seaming Methods for Various
Geomembranes 20
7.1 Temperature Ranges for Hot Wedge Seaming of Thermoplastic
Geomembranes 70
8.1 Typical Temperature Ranges for Hot Air Seaming of
Geomembranes 93
xv
-------
ACKNOWLEDGEMENTS
This technical guidance document grew out of a series of meetings of
various manufacturers of geomembranes. Drafts were reviewed by the
manufacturers, fabricators and installers of geomembranes, private consultants
and owners of waste management facilities. Robert M. Koerner, Director of the
Geosynthetic Research Institute, was the project coordinator who extends
sincere appreciation for the cooperation of this group of organizations in
sharing information and critiquing the various drafts of the document.
The EPA project manager of this technical guidance document was
Robert E. Landreth with the assistance of David A. Carson. The authors wish
to thank Donna A. Zunt, the preparer of the manuscript.
xv i
-------
SECTION 1
INTRODUCTION AND AUDIENCE
The lining and capping of hazardous and nonhazardous solid waste
landfills, surface impoundments and waste piles is a critical component in the
prevention of contamination of subsurface soil and groundwater. When a solid
or liquid contaminant is being contained, every aspect of the lining and
capping system must undergo the closest possible scrutiny. The need for both
construction quality control (CQC) and construction quality assurance (CQA)
becomes requisite at many facilities. With an extremely large number of waste
management construction and closure projects currently being planned and/or
already under construction there also comes many organizations with a lack of
experience in specialized topics. Certainly an area such as geomembranes made
from thermoplastic polymers falls into this category. Many inspection firms
entering into this area have had little formal training or practical
experience in dealing with geomembranes. This is not to say that experienced
firms are not available; they are indeed, and are very active in providing
excellent inspection services. However, there appears to be a need to have a
primer on certain aspects of geomembrane seaming which this document will
fulfill.
This manual is very narrowly focused, addressing only one part of the
total liner or final cover systems, that being field seaming methods for
geomembranes. This manual assumes that the design has been completed and the
material has been selected based on site specific functions and conditions.
In this report all types of currently used geomembrane materials will be
considered. They will be viewed with their customary method of seaming, and
not from a materials classification. For example, for the hot wedge seaming
method, focus will be on the idiosyncrasies of the method not the fact that
most geomembranes can be seamed by this method. When information is required
to distinguish between details such as seaming temperature from one
geomembrane to another, it will be elaborated upon accordingly. Still
further, it is the making (or fabrication) of the seams which will be the
focus, not their destructive or nondestructive testing. There are numerous
excellent documents on this latter topic, see, for example, Frobel (1), Lord,
et al. (2), Overmann (3) Richardson (4), Haxo and Kamp (5), Peggs (6), etc.
This Technical Guidance Document is primarily intended for engineering
organizations performing third-party inspection of geomembrane field seams.
This activity falls under the category of Construction Quality Assurance
(CQA). It is generally performed by engineering design firms, engineering
testing organizations and (occasionally) by manufacturer/installers who are
separated from the Construction Quality Control (CQC) activities. The
document has obvious overlaps with both public and private owner/operator
-------
concerns and can be used to amplify and extend their standard CQC/CQA
Documents on an as-required basis.
When using the document for the first time, the reader should become
familiar with the introductory material included in Sections 1 to 4. In these
sections various clarifications of terminology, definitions, departures from
current practice and other matters are described. Following this introductory
material, however, the user should proceed directly to the section on field
seaming that is of direct interest. Each of these sections, i.e., Section
Nos. 5 to 10, are written in a "stand-alone" fashion. Thus repetition within
these different sections was necessary to avoid "flip-flopping" between
sections. Of course, if one cares to read the manual in its entirety, it
becomes a tutorial on all of the currently available geomembrane seaming
methods. Section 11 pertains to seaming technologies currently under
development.
This Technical Guidance Document provides a field CQA person with a
readily accessible set of details of the essential aspects of the field
seaming procedure under concern. It also provides, in as much as possible,
the explanation for stating these details. By following its guidance it is
hoped that the manual's user will be better aware of what the installer is
trying to achieve and the rationale for performing any specific activity. The
document does not purport to be an installers procedural manual on how to
physically make geomembrane field seams. There are numerous CQC manuals
available by manufacturer/installer organizations as well as owner/operator
organizations for that purpose.
-------
FIELD NOTES:
-------
FIELD NOTES:
-------
SECTION 2
CONSTRUCTION QUALITY ASSURANCE CONCEPTS
As written in EPA Report 600/2-88/052 entitled "Lining of Waste
Containment and other Impoundment Facilities" (7) construction quality
assurance (CQA) is a planned system of activities that provides assurance that
the unit is constructed as specified in the design. Thus, CQA refers to those
activities initiated by the owner of the facility to ensure that the
construction of the entire facility, including manufacture, fabrication, and
installation of the various components of the lining and final cover systems,
meets design specifications and performance requirements. The activities
include inspections, verifications, audits, and evaluations of materials and
workmanship necessary to determine and document the quality of the constructed
facility. These activities are often performed by an owner/operator contracted
third-party quality assurance team that is independent of the designer,
manufacturer, fabricator, and installer to ensure impartiality.
It should be noted that Construction Quality Control (CQC) and
Construction Quality Assurance (CQA) are often loosely used terms covering the
entire range of construction activities. They are, however, used quite
rigorously in this Technical Guidance Document.
• Construction Quality Control (CQC), or simply Quality Control, refers
to activities conducted by the manufacturer and/or installer to bring
to bear the highest quality construction activities for the situation
under concern. In this manual, it is the fabrication of geomembrane
field seams. There often will be a separate document to define and
elaborate on the various details. This document is usually developed
"in-house", in that it is voluntarily offered to show the degree of
seriousness to which the manufacturer/installer intends to go about
the construction of the geomembrane field seams. It will be referred
to as the "CQC Document."
• Construction Quality Assurance (CQA), or simply Quality Assurance,
is completely separate from CQC. It cannot be done by the same
individuals or even the same organizations. It is often referred
to as "third party" inspection suggesting that an organization, or
persons, not affiliated with the owner/operator or manufacturer/
installer is performing the inspection activities. This is the
intended audience for this Technical Guidance Document. The
formation of such a CQA activity, and the role it has in the
inspection of geomembrane field seams, is defined in a document
which will be referred to in this manual as the "CQA Document."
CQC and CQA will obviously overlap in many instances. The ultimate
-------
case geomembrane field seams. The separate documents, referred to
herein collectively as "CQC/CQA Documents," should be synchronized
with one another. Any differences between the two documents, or
between these two documents and the contract plans and
specifications must be addressed at a Pre-Construction meeting. All
parties involved must be aware that this Pre-Construction meeting is
where the "ground rules" for construction will occur and all parties
will thereafter perform and act accordingly.
Regarding the elements of a CQC/CQA Document, EPA Report 530-SW-86-031
(NTIS PB87-132825) entitled "Construction Quality Assurance for Hazardous
Waste and Land Disposal Facilities" (8) presents the following key elements:
• Responsibility and Authority - The responsibility and authority of
organizations and personnel involved in permitting, designing, and
constructing the facility should be described in the CQC/CQA
Documents.
• CQA Personnel Qualifications - The qualifications of the CQA
officer and supporting CQA inspection personnel should be presented
in the CQC/CQA Documents.
• Inspection Activities - The observations and tests that will be
used to ensure that the construction or installation meets or
exceeds all design criteria, plans, and specifications for each
component should be described in the CQC/CQA Documents.
• Sampling Strategies - The sampling activities, sample size, methods
for determining sample locations, frequency of sampling, acceptance
and rejection criteria, and methods for ensuring that corrective
measures are implemented should be presented in the CQC/CQA
Documents.
• Documentation - Reporting requirements for CQA activities should be
described in detail in the CQC/CQA Documents.
This particular guidance document focuses on one specific aspect of CQA
namely the inspection of the fabrication of field seams used in the joining
of the most commonly used geomembranes.
-------
FIELD NOTES:
-------
FIELD NOTES:
-------
SECTION 3
TERMINOLOGY AND PREPARATORY ISSUES
The design of a geomembrane for a lined facility involves a substantial
amount of work before the actual construction is performed. In order that
the reader understands and appreciates the importance of some of these
preactivities, it was felt that a section on historical and future
perspectives, including assumptions, was needed. The authors have also
attempted to standardize or clarify terminology to more accurately reflect
current industry practice.
3.1 TERMINOLOGY
Many polymers commonly used in the manufacture of geomembranes,
previously called flexible membrane liners (FML), have been inaccurately
named, titled and described. Polymeric resins and processing methods evolve
over time to provide products that will serve their intended design function
better over long periods of time. As more products become available, it is
important to understand the proper descriptions for various polymeric
geomembrane materials.
In current practice, the term "high density polyethylene (HOPE)" is
used to describe geomembranes whose base resin may actually be medium
density polyethylene (MDPE). There are several resins of different
densities currently used in the manufacture of polyethylene geomembranes,
see Table 3.1.
The density ranges on Table 3.1 are for the basic polymer, i.e. the
resin, before addition of carbon black and other additives to either
increase performance and durability or assist in production. This document
will utilize the ASTM designation HOPE to reflect the material in use today.
Very low density polyethylene (VLDPE) resin falls into the density range
below 0.910 g/cc and is not yet designated by ASTM.
Some geomembrane sheets are compounded versions of relatively rigid
thermoplastic polymers, such as polyvinyl chloride (PVC). Other
geomembranes are compounded versions of elastomers, such as chlorosulfonated
polyethylene (CSPE). Each is formulated with specific expectations in mind
ranging from long-term flexibility, to long-term weatherability, to cost.
The authors will utilize the terminology "compounded thermoplastic" or
"thermoplastic elastomers" to reflect the actual material in use today.
Table 3.2 lists several of these liner materials that are in current use.
-------
TABLE 3.1. POLYETHYLENE TYPES.
Acronym
HOPE
HOPE
MDPE
LDPE
Type
High Density Polyethylene
High Density Polyethylene
Medium Density Polyethylene
Low Density Polyethylene
Not designated
Nominal
Density Range
> 0.960 g/cc
0.941 to 0.959 g/cc
0.926 to 0.940 g/cc
0.910 to 0.925 g/cc
< 0.910 g/cc
ASTM
D 1248
Type
IV
III
II
I
0
* Uncolored, unfilled material
TABLE 3.2. COMPOUNDED THERMOPLASTICS AND THERMOPLASTIC ELASTOMERS.*
PVC EIA
PVC-R** EIA-R
CPE CSPE
CPE-R CSPE-R
See Section 13, Glossary of Terms for definitions.
"R" denotes fabric reinforced geomembrane.
Resins used in pipes, fittings and appurtenances are generally
significantly different from those used in the manufacture of geomembranes.
While prefabricated boots may make installation more convenient, it may not
be possible to seam geomembranes directly to these other items. Further,
the junction is generally fortified with a mechanical connection to ensure a
flexible watertight bond. These details must be clearly stipulated in the
CQA/CQC Documents.
One of the fundamental methods of joining polymer geomembrane sheets is
with a chemical processes of chemical fusion or chemical-adhesive methods.
Commonly referred to as "solvent welding," or "solvent seaming," a more
generic term "chemical bonding" will be used in this document. The methods
10
-------
and materials used to perform this type of bonding can vary widely, and may
vary in accordance with site conditions. The designer should evaluate these
variances and incorporate them into the CQC/CQA Documents.
Workers and inspectors should protect themselves from long-term
exposure to the chemicals present during any installation. The safety
precautions printed on the labels of all chemicals should be followed.
Personal protective equipment should exceed the minimal requirements listed
on the labels. Material Safety Data Sheets should also be reviewed prior to
exposure. State and local safety regulations should be followed.
Workers and inspectors should also be aware that some seaming devices
can and do get very hot. These devices require the use of extension cords
which could cause personnel to trip and fall. Hot air/gas seaming devices
or other air blowing devices may cause dirt to be blown into eyes. All
appropriate state and local safety regulations should be followed.
Following conventional usage, the term "hot air" has been used when
speaking of the process involving hot gas to seam geomembrane sheets.
Certain unusual circumstances may require the use of an alternate heat
conveyance gas other than air. The use of such an alternative must be
clearly stated in the CQC/CQA Documents.
3.2 PREPARATORY ISSUES
This document is intended to provide guidance for the inspection of
geomembrane seams being fabricated in the field. To this end, several
assumptions have been made regarding the actual material brought or
delivered to the installation site. This document assumes that the facility
design has been completed, the material has been selected based on specific
site functions and conditions and that CQC/CQA Documents have been
developed.
Inherent in these broad assumptions are the following items:
(1) The designer should prequalify the material and seaming
technique, before the actual installation, and include in the
CQC/CQA Documents evaluation procedures to verify the quality of
the actual seams. In these cases such concerns as stress
cracking and/or chemical resistance of the geomembrane sheet and
seams, or percentage of full seam strength could be resolved.
The prequalifying period may also be used to correlate
accelerated (e.g. oven) aging of chemical seams with full seam
strength without acceleration. However, these prequalification
tests are to be used only for general acceptance as the actual
field seam should be accepted/rejected based on actual field
samples based on the CQC/CQA Documents.
(2) The soil subgrade has been prepared such that no rocks, sticks,
sudden elevation changes, etc., are present to damage the
geomembrane sheet by puncturing from below or from damage
11
-------
resulting from installation personnel walking or equipment (e.g.,
rubber tired generators) being on top of the geomembrane.
(3) The design considered the appropriate thickness of the material
being installed. This includes but is not limited to: minimum
regulatory material requirements; thickness variation due to
manufacturing; thickness changes due to material preparation
(grinding or softening geomembrane surface layers) and design
requirements. It is recognized that the seam areas can be the
weak points in the geomembrane system. The design should consider
the above factors independently and jointly as they may result in
stress concentrations.
(4) The facility design includes consideration for durability of the
material. Service life of the geomembrane may be affected by seam
cracking or mechanical fatigue that may cause cracking or
catastrophic failure; swelling and softening of polymeric
components due to absorbed waste constituents combined with an
overburden load that may cause creep-induced damage; and
extraction, volatilization, or biodegradation of additives in the
compounds due to long-term exposure that may cause degradation of
polymeric materials.
(5) The design has taken site specific conditions such as potential
temperature and humidity into consideration when selecting the
geomembrane material to be installed and the actual seaming
technique to be used at that specific site. When seaming
geomembrane sheet it is actually the sheet temperature that
influences the quality of the seam. It is, therefore, recommended
that geomembrane sheet temperature be measured rather than ambient
temperature.
(6) It is also recognized that moisture can cause a detrimental effect
on seam quality. In those cases where chemicals are used to make
the seam the designer should understand that the process of
evaporation of the chemical involves the consumption of heat (heat
of vaporization) from the geomembrane being seamed and thus can
cool the geomembrane surface resulting in moisture condensation in
the seam area when the relative humidity is high. The point is
that temperature and humidity at the time of installation may
affect the selection of the chemical mixture used. This same heat
phenomenon will also cause condensation in seam areas for hot
wedge and extrusion welds.
(7) Grinding of sheet edges in preparation for extrusion welding
should always be done to leave marks perpendicular to the sheet
edge, to the extent possible. Insufficient data exists to
definitively determine whether all grind marks should be covered.
It is generally recognized that they should, but it is also known
that extrudate over unground area will not form a good bond. The
designer should specify or recommend which procedure will be
acceptable and how to evaluate this through the CQC/CQA Documents.
12
-------
(8) The number and spacing of destructive tests in production seams
has been clarified and stipulated in the CQC/CQA Documents. This
includes the length of the destructive test sample, how sections
are distributed, when and to whom test results are due, and
acceptance/rejection criteria.
(9) The CQC/CQA Documents should be very specific when new to old
sheets are being seamed in the field, when different thicknesses
of the same sheet are being seamed together, when different
materials are seamed together (e.g. PVC and CSPE, VLDPE and HOPE,
etc.), when sheet is bonded or joined to pipes, manholes, and/or
other appurtenances, or for other unusual conditions.
(10) The design and CQC/CQA Documents have determined the number,
length, distribution and testing of seam test strips. One could
envision individual samples for the owner/operator for site
approval, the geomembrane manufacturer, for archive purposes and
for the regulatory community. All of these requirements may
result in test strip lengths from 1.5 to 4.5 m (5 to 15 ft.) or
more. The length should be determined based on which ASTM test
will be used for seam evaluation as well as the number of
interested parties; in any case the total length should be
specified in the CQC/CQA Documents. The implications of failure
of these test strips must be clearly understood by all parties.
3.3 UNITS
In past EPA documents, all dimensions in the text, tables and figures
have been traditional, or English units, i.e., the "foot-pound-degree
Fahrenheit" system of measurement. The future, as we all know, is toward
the use of metric units, i.e., the "meter-gram-degree Centigrade" system.
This latter system has been slightly revised into the ("Systeme
Internationale d'Unit£s") units or simply "S.I." units and is rapidly being
accepted on a worldwide basis.
This manual is written in dual units with the S.I. units as the
preferred units and the standard units following in parenthesis. It is more
than likely that future EPA documents will be in S.I. units only, thus a
complete familiarization will eventually be necessary.
A word of explanation as to unit of length is necessary. The S.I. unit
of length is the millimeter (mm). Recognize that it is a very small value,
i.e., 1 mm - 0.04 inches. Thus the coverage of a 6 inch patch over a hole
in a geomembrane would convert to 150 mm. Note that the tolerance of this
value should be considered equivalently, i.e. we are not inferring a
tolerance of 1 mm, but the usual tolerance of say 1 inch which would be
approximately 25 mm. Thus to ease the unfamiliar reader into S.I. units we
have written the text in centimeters so as to take the customary values of
tolerance into account. The figures, however, have been labeled in
13
-------
millimeter and meter units which are the recommended S.I. values to use and
rounded for convenience.
With regular use of S.I. units and thinking in this manner, the
differences between mm, cm, and m values will become routine.
3.4 TEST STRIPS
Test (or trial) strips, also called qualifying seams, are considered to
be an important aspect of CQC/CQA procedures. They are meant to serve as a
prequalifying vehicle for personnel, equipment and procedures for making
seams under identical material and climatic conditions as will be the actual
production field seams. The test strips are usually made on two narrow
pieces of excess geomembrane varying in length between 1.5 to 4.5 m (5 to 15
ft.). The test strips should be made in sufficient lengths, preferable as a
single continuous seam, for all required purposes.
The goal of these activities is to imitate all aspects of the actual
production field seaming activities intended to be performed in the
immediately upcoming work session to estimate seam quality. Ideally, test
strips can estimate the quality of the production seams while minimizing
damage to the installed geomembrane through destructive mechanical testing.
They are typically made every 4 hours (for example, at the beginning of the
work shift, after the lunch break) or whenever personnel or equipment
changes and when climatic conditions reflect wide changes in geomembrane
temperature (±5°C [± 9° F] change in one hour) or other conditions that
could affect s2eam quality. These details, including the minimum level of
destructive testing of the production field seams should be stipulated in
the Contract Specifications or CQC/CQA Documents.
The destructive testing of the test strips in shear and peel should be
done as soon as the installation contractor feels that the strength
requirements of the Contract Specification or CQA/CQA Documents can be met.
This is generally done at the site using a field tensiometer. Thus it
behooves the contractor to have all aspects of the test strip seam
fabrication in complete working order just as would be done in the case of
fabricating production field seams.
In the flow chart following it is seen that failed test strips are
linked to an increased frequency of destructive tests to be taken on
production field seams made during the time interval between making the test
strip and its testing. Furthermore, it is seen that there are only two
chances at making adequate test strips before production field seaming is
stopped and repairs are initiated. The specifics of these repairs are not
defined in this document. They should be covered in either the Contract
Specification or the CQC/CQA Documents.
Additional text for conducting these tests is located in each of the
specific seam focused sections and generally follows the activity pattern
described in Figure 3.1.
14
-------
•Not*: Stunlng dm filling Ib Pnpir*
Acctplfb/* TtitStrtptMlyRiqvtn
ROnlnlng In Aecoaltnct wHn CQC/COA Daeumum
Figure 3.1 Test strip process flow chart.
15
-------
FIELD NOTES:
16
-------
SECTION 4
AN OVERVIEW OF FIELD SEAMING METHODS
The fundamental mechanism of joining polymer geomembrane sheets is to
temporarily reorganize the polymer structure of the two surfaces in a
controlled manner (i.e. melt or soften) that, after the application of pressure
and after the passage of a certain amount of time, results in the two sheets
being bonded together. This reorganization results from an input of energy
that originates from either chemical or thermal processes. These processes may
involve the addition of extra polymer in the bonded area.
Ideally, seaming two geomembrane sheets would result in no net loss of
tensile strength across the two sheets and the joined sheets would perform as
one single geomembrane sheet. However, due to stress concentrations resulting
from the seam geometry, current seaming techniques may result in minor tensile
strength loss compared to the parent geomembrane sheet. The characteristics of
the seamed area are a function of the type of geomembrane and the seaming
technique used. These factors, such as residual strength, geomembrane type,
and seaming type, should be recognized by the designer when applying the
appropriate design factors of safety for the overall geomembrane function and
facility performance.
It should be noted that the seam can be the location of the lowest tensile
strength in a geomembrane liner. Designers and inspectors should be aware of
the importance of seeking only the highest quality geomembrane seams. The
minimum seam tensile strengths (as determined by design) for various
geomembranes must be predetermined by laboratory testing, knowledge of past
field performance, manufacturers literature, various trade journals or other
standard setting organizations that maintain current information on seaming
techniques and technologies.
The methods of seaming at the time of the printing of this document and
discussed herein are shown in Table 4.1.
Within the entire group of thermoplastic geomembranes that will be
discussed in this manual, there are four general categories of seaming methods:
extrusion welding, thermal fusion or melt bonding, chemical fusion and
chemical adhesive seaming. Each will be explained along with their specific
variations so as to give an overview of field seaming technology.
Extrusion welding is presently used exclusively on geomembranes made from
polyethylene. A ribbon of molten polymer is extruded over the edge of, or in
between, the two surfaces to be joined. The hot extrudate causes the surfaces
of the sheets to become hot and melt, after which the entire mass then cools
and bonds together. The technique is called extrusion fillet seaming when the
17
-------
TABLE 4.1. FUNDAMENTAL METHODS OF JOINING POLYMERIC GEOMEMBRANES
Thermal Processes Chemical Processes
Extrusion Fillet (Ch. 5) Chemically Fused:
Extrusion Flat (Ch. 6) . Chemical (Ch. 9)
Hot Wedge (Ch. 7) . Bodied Chemical (Ch. 9)
Hot Air (Ch. 8) Chemical Adhesive (Ch. 10)
extrudate is placed over the leading edge of the seam, and is called extrusion
flat seaming when the extrudate is placed between the two sheets to be joined.
It should be noted that extrusion fillet seaming is essentially the only method
for seaming polyethylene geomembrane patches and in poorly accessible areas
such as sump bottoms and around pipes. Temperature, pressure, and seaming rate
all play important roles in obtaining an acceptable bond; too much melting
weakens the geomembrane and too little melting results in inadequate flow
across the seam interface and in poor seam strength. The polymer used for the
extrudate is also very important and is usually the same polyethylene compound
that was used to made the geomembrane. The designer should specify acceptable
extrusion compounds and how to evaluate them in the CQC/CQA Documents.
There are two thermal fusion or melt-bonding methods that can be used on
all thermoplastic geomembranes. In both of them, portions of the opposing
surfaces are truly melted. This being the case, temperature, pressure, and
seaming rate all play important roles in that too much melting weakens the
geomembrane and too little melting results in poor seam strength. The hot
wedge or hot shoe method consists of an electrically heated resistance element
in the shape of a wedge that travels between the two sheets to be seamed. As
it melts the surface of the sheets being seamed, a shear flow occurs across the
upper and lower surfaces of the wedge. Roller pressure is applied as the two
sheets converge at the tip of the wedge to form the final seam. Hot wedge
units are automated as far as temperature, amount of pressure applied and
travel rate. A standard hot wedge creates a single uniform width seam while a
dual hot wedge (or "split" wedge) forms two parallel seams with a uniform
unbonded space between them. This space can be used to evaluate seam quality
and continuity of the seam by pressurizing the space with air and monitoring
any drop in pressure that may signify a leak in the seam.
18
-------
The hot air method makes use of a device consisting of a resistance
heater, a blower, and temperature controls to blow hot air between two sheets
to melt the opposing surfaces. Immediately following the melting of the
surfaces, pressure is applied to the seamed area to bond the two sheets. As
with the hot wedge method both single and dual seams can be produced. In
selected situations, this technique will be used to temporarily "tack" weld two
sheets together until the final seam or weld is accepted.
Regarding the chemical fusion seam types; chemical fusion seams make use
of a liquid chemical applied between the two geomembrane sheets to be joined.
After a few seconds to soften the surface, pressure is applied to make complete
contact and bond the sheets together. As with any of the chemical seaming
processes to be described, a portion of the two adjacent materials to be bonded
is truly transformed into a viscous phase. Too much chemical will weaken the
adjoining sheet, and too little chemical will result in a weak seam. Bodied
chemical fusion seams are similar to chemical fusion seams except that 1-10% of
the parent lining resin or compound is dissolved in the chemical and then is
used to make the seam. The purpose of adding the resin or compound is to
increase the viscosity for slope work and/or adjust the evaporation rate of the
chemical. This viscous liquid is applied between the two opposing surfaces to
be bonded. After a few seconds, pressure is applied to make complete contact.
Chemical adhesive seams make use of a dissolved bonding agent (an adherent)
which is left after the seam has been completed and cured. The adherent thus
becomes an additional element in the system. Contact adhesives are applied to
both mating surfaces. After reaching the proper degree of tackiness, the two
sheets are placed on top of one another, followed by roller pressure. The
adhesive forms the bond and is an additional element in the system.
Other emerging seaming methods use ultrasonic, electrical conduction and
magnetic induction energy sources. Since these methods are in a development
stage, they are included in a separate section entitled, "Emerging Technologies
for Geomembrane Seaming."
In order to gain an overview as to which seaming methods are used for the
various thermoplastic geomembranes described in this document, Table 4.2 is
offered. It is generalized, but it is used to further introduce the six
specific seaming methods to be described in the following sections.
19
-------
TABLE 4.2. MOST COMMONLY USED FIELD SEAMING METHODS FOR VARIOUS GEOMEMBRANES.
Type of Seaming
Method
Type of Geomembrane
CPE CPE-R CSPE-R EIA EIA-R HOPE PVC PVC-R VLDPE
extrusion fillet n/a n/a n/a n/a n/a A n/a n/a A
extrusion flat
hot air
hot wedge
chemical
adhesive
n/a n/a n/a n/a n/a A n/a n/a A
A n/a A A n/a
A n/a A An/a
Note: A = method is applicable
n/a = method is "not applicable"
20
-------
FIELD NOTES:
21
-------
FIELD NOTES:
22
-------
SECTION 5
DETAILS OF EXTRUSION FILLET SEAMS
As seen in Table 4.2, extrusion fillet seaming is an applicable seaming
method for HOPE and VLDPE geomembranes. In fact, around details such as
pipes and sumps it is always necessary to use a certain amount of extrusion
fillet seaming. This method is also used for repairs. Thus the text in this
section is written with HOPE and VLDPE geomembranes in mind.
5.1 GEOMEMBRANE PREPARATION
(a) Note, that this document assumes that the proper geomembrane has
been visually inspected to ensure that the sheet is free of deep
scratches or defects that would cause the sheet to not meet the
specifications of the installation. It is further assumed the
sheet has been delivered to the site and brought to its
approximate plan position for final installation and seaming.
Only the material that can be seamed that day should be deployed.
All deployed material should be adequately ballasted to prevent
wind uplift.
(b) The geomembrane, HOPE or VLDPE, will usually arrive on site in
rolls.
(c) The geomembrane should remain packaged or rolled and dry until
ready to use. The material should not be unrolled if the material
temperatures are lower than -10°C (14°F) due to the possibility of
cracking. If the panel is stored in a warm place, e.g. 10°C
(50°F) or above, prior to being unrolled on site, then it can be
placed at -18°C (0°F) or below temperatures providing the time
between removing the geomembrane from storage and deployment does
not exceed one-half working day. Geomembrane deployment may be
allowed under other conditions but the CQC/CQA Documents and/or
project specifications must be specific as to the conditions.
(d) The two geomembrane sheets to be joined must be properly
positioned such that approximately 7.5 cm to 15.0 cm (3 to 6
inches) of overlap exists.
(e) All personnel walking on the geomembrane should have smooth soled
shoes. Heavy equipment, e.g. pickups, tractors, etc., should not
be allowed on the geomembrane at any time, unless otherwise
specified by the manufacturer and approved in the CQC/CQA
Documents.
23
-------
I
(f) If the overlap is insufficient, lift the geomembrane sheet up to
allow air beneath it and "float" it into proper position. Avoid
dragging geomembrane sheets made from HOPE particularly when they
are on rough soil subgrades since scratches in the material may
create stress points of different depths and orientations.
(g) If the overlap is excessive and is to be removed, it should be
done by trimming the lower sheet only. If this is not possible
and the upper sheet must be trimmed, do not use a knife with an
unshielded blade to cut off the excessive amount because the blade
facing downward can easily scratch the underlying geomembrane in a
very vulnerable location. A shielded blade or a hook blade should
be used to trim off the excess geomembrane. A photograph of such
a device is shown in Figure 5.1. Whenever possible it should be
used from beneath the liner in an upward cutting motion.
Figure 5.1. Type of hook blade used for the cutting of liner materials.
(h) All cutting and preparation of odd shaped sections or small fitted
pieces should be completed at least 15 m (50 ft.) ahead of the
seaming operation so that seaming may be continued with as few
interruptions as possible.
(i) Visually check the two opposing geomembrane sheets to be joined
for defects of sufficient magnitude to affect seam quality. The
criteria to be met and the procedures to be used in this regard
should be stipulated in the contract specifications and/or in the
CQC/CQA Documents.
24
-------
(j) If the Construction Plans require overlaps to be shingled in a
particular direction, this should be checked.
(k) Excessive undulations (waves) along the seams during the seaming
operations should be avoided. When this occurs due to either the
upper or lower sheet having more slack than the other or because
of thermal expansion or contraction, it often leads to the
undesirable formation of "fishmouths" which must be trimmed, laid
flat and reseamed with a patch.
(1) There should be some slack in the installed liner, which depends
on the type of geomembrane, the ambient and anticipated service
temperatures, length of time the geomembrane will be exposed,
location in the facility, etc. This is a design consideration and
the Contract Plans and Specifications must be project specific on
the amount and orientation of slack.
(m) The sheets which are overlapped for seaming must be clean. If
dirty, they must be wiped clean with dry rags or other appropriate
materials.
(n) The sheets which are overlapped for seaming must be completely
free of moisture in the area of the seam. In the case of
moisture, air blowers are usually preferred over rags for drying
the geomembrane.
(o) Seaming is not allowed during rain or snow, unless proper
precautions are made to allow the seam to be made on dry
geomembrane materials, e.g., within an enclosure or shelter.
(p) It is preferable not to have water-saturated soil beneath the
geomembrane during installation. Seaming boards help in this
regard by lifting the seams off the soil subgrade.
(q) If the soil beneath the geomembrane is frozen, the heat of seaming
can thaw the frost possibly allowing water to condense on the
unbonded region ahead of the seam being fabricated. This
possibility may be eliminated by the use of suitable seaming
boards or slip sheets made from excess pieces of geomembrane.
(r) The temperature of the geomembrane for seaming should be above
freezing, i.e. O'C, (32°F) unless it can be proven with test
strips that good seams can be fabricated at lower temperatures.
However, temperature is less a concern to good seam quality than
is moisture.
(s) For cold weather seaming, it may be advisable to preheat the
sheets with a hot air blower, to use a tent of some sort to
prevent heat losses during seaming and to make numerous test
strips in order to determine appropriate seaming conditions, e.g.,
equipment temperatures may have to be set higher and seaming rates
slowed down during cold weather seaming.
25
-------
I
(t) Sheet temperatures for seaming should be below 50"C (122°F) as
measured by an infrared thermometer or surface contact
thermocouple. It is recognized that depending on material type
and thickness, higher temperatures may be allowed. It should also
be recognized that wind and cloud cover will determine the actual
sheet temperature. High temperatures affect not only worker
performance but will also effect durability of some geomembranes
unless special precautions, e.g. tents, etc., are taken. For
temperatures above this value special attention should be paid to
the seaming operation. Frequent test strips and more diligent
nondestructive testing is recommended.
NOTE: For items (q), (r), (s,) and (t) the CQC/CQA Documents
and/or project specifications and the regulatory requirements
regarding hot and cold temperature seaming limitations should be
reviewed to avoid possible problems with final construction
certification acceptance.
5.2 EQUIPMENT PREPARATION
(a) Properly functioning portable electric generators must be
available within close proximity of the seaming region and with
adequate extension cords to complete the entire seam. These
generators should be of sufficient size or numbers to handle all
seaming electrical requirements. The generator must have rubber
tires, or be placed on a smooth plate such that it is completely
stable so that no damage can occur to the geomembrane or to the
underlying clay liner or subgrade material. Fuel (gasoline or
diesel) for the generator must be stored away from the geomembrane
and if accidently spilled on the geomembrane it must be
immediately removed. The area should be inspected for damage to
the geomembrane and repaired if necessary.
(b) An electric rotary grinder having a grinding disk of approximately
10 cm (4 inch) in diameter and a sufficient quantity of #80 grit
paper must be available, see the photograph in Figure 5.2. Also
acceptable is #100 grit paper which is finer than #80. Sandpaper
coarser than #80, e.g. #60, is not acceptable. Caution should be
used to prevent overgrinding.
(c) A hot air welder with temperature capability to 250°C (475'F)
must be available to periodically tack weld the geomembrane sheets
after they are properly positioned. The hot air tacking should
not be strong enough to produce a film tearing bond or interfere
with the testing of the seam in either peel or shear.
Occasionally, double-sided tape is used to temporarily anchor two
sheets to be seamed. This practice is not recommended unless the
tape is placed sufficiently far from the seam itself to ensure
that it will not get to the seam area.
26
-------
Figure 5.2. Hand-held electric rotary grinder with
circular disc grit grinding paper.
(d) The extrusion fillet welding apparatus may be of two types,
depending upon the location where the seams are to be made.
Either rubber wheeled, automated seam extruders or hand-held
portable extruders are available. Photographs of various systems
are shown in Figure 5.3.
(e) All extrusion fillet seaming devices must be equipped with
properly functioning temperature controllers displaying the
temperature in the extrusion barrel so that it may be monitored by
seaming personnel. It is recommended that the temperature of the
extrudate be periodically made to check the reading of the
thermocouple permanently mounted on the barrel. The CQC/CQA
Documents should be reviewed for appropriate temperature ranges.
(f) Extrusion fillet seaming devices have various Teflon or metal dies
of different shapes and sizes where the extrudate exits onto the
geomembrane. These dies must be inspected for wear, sharp notches
or creases, and for correctness for the particular application.
Commercially available extrusion dies are available for most
common geomembrane thicknesses. Many, however, are specifically
made or modified by installers. Both the width and thickness of
the extrudate are dependent upon the proper die. It should be
noted that nozzle selection will vary with geomembrane thickness.
27
-------
Figure 5.3. Photographs of various types of extrusion fillet welding
devices.
Upper: Automated type
Lower: Hand-held type
28
-------
(g) Adequate extrudate welding rods or pellets, of the same
composition as the geomembrane itself, must be used. They must be
dry, clean and ready for feeding through the extruder. All
extrudate resin must be properly formulated so as to be the same
compound as the geomembrane sheet material. Manufacturers may be
required to provide a certification letter indicating that the
welding rod or pellets and the sheet are the same compound. If in
doubt, verification methods must be performed, see Reference 7.
All extrudate material must be kept dry and free of dirt, debris
and foreign matter. When welding rod is used the size must be
consistent and appropriate for the seaming device.
5.3 TEST STRIPS
A general requirement of most CQA Documents is that "test seams" or
"test strips" be made on a periodic basis. Test strips generally reflect the
quality of field seams but should never be used solely for final field seam
acceptance. Final field seam acceptance should be specified in the contract
specification and should include a minimum level of destructive testing of
the production field seams. Test strips are made to minimize the amount of
destructive sampling/testing which requires subsequent repair of the final
field seam. Typically these test seams, for each seaming crew, are made
about every four hours, or every time equipment is changed, or if significant
changes in geomembrane temperature are observed, or as required in the
contract specification. This is a recommended practice that should be
followed when seaming all types of geomembranes. The purpose of these tests
is to establish that proper seaming materials, temperatures, pressures,
rates, and techniques along with the necessary geomembrane pre-seaming
preparation is being accomplished. Test strips may be used for CQA/CQC
evaluation, archiving, for exposure tests, etc., and must be of sufficient
length to satisfy these various needs.
Each seaming crew and the materials they are using must be traceable and
identifiable to their test seams. While the test seams are being prepared,
cured, and CQC tested, the seaming crew may continue to work as long as the
seams they have made (and are making) since their last acceptable test sample
strip was prepared, are completely traceable and identifiable. If a test
seam fails to meet the field seam design specification, then an additional
test seam sample will have to be made by the same seaming crew - using the
same tools, equipment and seaming materials - and retested.
The liner's finished field seams will not be accepted unless the before
and after "test seam sample strip" CQC test results (or other CQC seam test
result criteria as required per the design specification) are acceptable per
the site's design specifications. If a seam is not accepted, destructive
testing of samples from the actual seam will be removed from the liner and
tested. If the actual seam destructive test results still do not meet the
design specification requirement, then the unacceptable seams will all have
to be repaired or reconstructed with seaming materials by a test proven
seaming crew that has passed its testing requirements. The procedure
illustrated in the flow chart of Figure 5.4 must be followed. Note that the
29
-------
•Not*: Sumlng Cnw filling to Pnatn
Acctpttblt Tttt Strip* Htyfitquln
attaining tiAeconfinct trlth CQC/CQA Documtntt
Figure 5.4. Test strip process flow chart.
30
-------
failure of test strip 1 requires two actions: (a) the making of test strip
2, and (b) an increased frequency of destructive tests on production field
seams made during the curing of test strip 1 (if any were made). This
increased frequency must be stipulated in the contract specifications or in
the CQC/CQA Documents.
If the destructive seams fail or if test strip 2 fails, production field
seaming is halted. All production field seams made during the interval are
repaired per the contract specifications or CQC/CQA Documents to the point of
previous acceptance with an approved seaming crew.
At this point, the seaming crew that failed to pass both strip tests
must adjust and recertify current seaming equipment and technique or obtain
new seaming equipment, tools and/or retrain personnel and begin making
initial test strip samples.
Test strips are shown in Figure 5.5(a-e). Figure 5.5(a) shows a sample
of the geomembrane being cut to form the two pieces to be seamed together.
Figure 5.5(b) shows the hot air tacking of the two pieces together so as to
maintain their respective positions. Figure 5.5(c) shows the grinding and
beveling of the leading edge for deposition of the extrudate. Figure 5.5(d)
shows the extrusion fillet seam being placed symmetrically over the edge of
the upper sheet. Figure 5.5(e) shows the completed test strip cut into three
sections and identified for the parties involved as per the CQC/CQA
Documents. For geomembranes that are seamed by extrusion or thermal methods
the seams can be tested after they are allowed to cool in ambient air at
least 5 to 10 minutes prior to peel and shear testing.
As previously stated, all seam test samples must be prepared in
triplicate sets from a single continuous test strip which can be cut into
thirds; one set for CQC tests, one set for CQA tests and one set made
available to (or retained for) the agency/owner/design organization. If
referee test results are required, CQA test results from destructive testing
of actual seam samples will prevail.
During the CQC and CQA test evaluation periods, a liner should not be
covered and it cannot be placed into service. This will insure that it is
available for repairing or reconstructing in the event it is required.
During this period it is imperative that the liner be properly ballasted or
otherwise secured so as to prevent wind or unusual weather damage.
5.4 ACTUAL SEAMING PROCESS
(a) Whenever HOPE geomembranes are 1.5 mm (60 mils) in thickness or
greater, the leading edge of the upper sheet must be ground to a
45" bevel. It is important that the sheet to be beveled is lifted
up off the lower sheet so that no grind marks whatsoever occur in
the lower sheet outside of the area to be seamed, see Figure 5.6.
Note that grinding should be done prior to tack welding in order
to exercise control against damage to the lower sheet.
31
-------
I
Figure 5.5(a). A polyethylene geomcmbrane sample being cut into two
sections for fabrication of the test strip.
Figure 5.5(b). The two sections of geomembrane being hot air "tacked"
so as to maintain their proper positioning and preventing
movement during seaming.
32
-------
Figure 5.5(c). Grinding of geomembrane surfaces to remove
surface oxides and waxes.
Figure 5.5(d). Placement of extrudate on the prepared polyethylene
geomembrane surface. Movement is from left to right
in the photograph.
33
-------
Figure 5.5(e). The completed test strip has been cut into three
sections and identified for the parties involved
to destructively test or archieve.
Grinding Wheel
Extreme care must be exercised
so that this surface is not
touched with grinding wheel
75 mm (3 in.) Min.
Figure 5.6. Preparing the bevel of the upper geomembrane for liner
thicknesses greater than 1.5 mm (60 mil.)
34
-------
(b) Following the preparation of the bevel, the upper sheet is lowered
and laid flat on the lower sheet and the horizontal surface
grinding of both upper and lower sheets is completed as shown in
Figure 5.7. All of the surface sheen in the area to be seamed
must be totally removed. Heavy textured grit sand papers coarser
than #80 size that leaves deep grooves that might become stress
points or leak channels are unacceptable. All of the material
that has been ground from the geomembrane sheets must be wiped or
blown away from the actual seaming zone.
^ Extrudate Width ^j
^ To Be C
12-25 mm
^ (0.5 - 1.0 in.) *
*^
Upper Geomembrane """""""'•*fy>
Covered
12 - 25 mm
(0.5 - 1.0 in.) *
*r\
f*7////SXS/lW//Ss
Lower Geomembrane
75 mm (3 in.JMin.
Surfaces To Be
Prepared By Grinding
Figure 5.7. Proper orientation and grinding preparation of sheets
prior to tacking and extrudate placement.
(c) The preferred orientation of grinding marks is perpendicular to
the seam direction rather than parallel to it. It should be
mentioned that this is a slow process for the installation
contractor to perform. The reasoning against parallel grinding is
that deep, parallel grooves decrease parent material thickness in
the direction of stress application across the seam and can lead
to seam failure in the parent material. Although the film tearing
bond criterion is usually satisfied, it is often at a reduced
stress due to the thinner material, see Figure 5.8 for the
distinction between the two different orientation patterns.
Please note that both grinding patterns in Figure 5.8 are
excessive and improper in their extent beyond the extrudate and
are shown for illustration purposes only.
(d) The depth of the grinding marks (whatever the direction) is of
paramount interest. Initial grinding depths should be targeted to
be less than 5% of the sheet thickness. Areas where grinding
depths are greater than 10% should not be incorporated into the
seam. The objective of grinding is to remove oxidized layers and
waxes from the geomembrane surfaces and to roughen the seam areas
of the sheets for bonding to the extrudate. The grinding should
yield a fine grained smooth surface. The amount of material
35
-------
Figure 5.8. Photographs of different orientations of grinding patterns.
Upper: Grind marks perpendicular to seams (recommended pattern)
Lower: Grind marks parallel to seam (not recommended pattern)
(Note, however, that both situations have grinding far in
excess of what is required and are shown for illustration of
the grinding patterns only, see Figure 5.9 following).
36
-------
removed by grinding should be minimal as only a nominal amount of
sheeting needs to be removed to achieve a new surface. Should
grind depth exceed 10% of sheet thickness, then the seam area must
be adjusted such that improperly ground area is not involved in
the seam or that improperly ground area should be physically
removed.
(e) Regarding the extent of the grinding, the general rule should be
that grinding marks should not appear beyond 0.6 cm (1/4 inch) of
the extrudate after it is placed, see Figure 5.9. Thus, if the
final extrudate bead width is 4.0 cm (1.5 in.) in width, the total
grinding pattern should be no more than 5.0 cm (2.0 in.), which is
equidistant on each side of the weld centerline.
(f) Grinding shall be completed no more than 10 minutes before seaming
takes place so that oxidized surface layers are not recreated
prior to placement of the extrudate and to prevent dirt from
embedding itself in the patterned grooves.
(g) The hand held grinder used for the grinding process must be turned
off whenever it is not in use. Never leave it running. If it
contacts the liner while running it will cause serious damage.
(h) Note that if the temporary tacking (refer to Section 5.2) is done
before the beveling and grinding operations described in steps (a)
through (g), then extreme caution against overgrinding and
mistakes must be taken. It might be necessary to provide a wedge
to lift up the overlying geomembrane as shown in Figure 5.10, or
to use a thin metal sheet with rounded corners and slide it along
the grinding area on top of the bottom sheet. If double sided
tape is used for temporary tacking, it should be placed far enough
from the edges to not interfere with the fusion process.
(i) The extrusion welder is to be purged of all aged extrudate in the
barrel prior to beginning a seam. This must be done every time
the extruder is restarted after a 2 min., or longer, period of
inactivity. The purged extrudate should not be discharged onto
the surface of previously placed liner nor on the prepared
subgrade where it would eventually form a hard lump under the
liner causing stress concentrations and possibly premature
failure.
(j) Extrudate in the form of a molten, highly viscous fluid is now
deposited over the overlapped geomembrane. The center of the
extrudate must be located directly over the edge of the upper
geomembrane. The extrudate should cover the grind marks on each
side of the upper and lower geomembranes to within 0.6 cm (1/4
inch) of the outside borders.
37
-------
Figure 5.9. Photographs of different extent of grinding patterns after
extrusion fillet seaming.
Upper: Excessive and irregular grinding beyond extrudate.
Lower: Acceptable grinding pattern just showing beyond
extrudate.
38
-------
Hot Air Tacking
Zone
Upper Geomembrane
(8888888S888888
Temporary
Propping
Wedge
Lower Geomembrane
Figure 5.10. Smooth propping wedge used when tacking of sheets is done
before surface grinding of the geomembrane sheets.
(k) The extrudate thickness should be approximately equal to or
greater than the specified sheet thickness measured from the top
of the upper sheet to the top or crown of the extrudate, see
Figure 5.11. Excessive squeeze-out (or flashing) as shown in the
lower sketch of Figure 5.11 is acceptable as long as it is
properly joined with the geomembrane, symmetric and will not
interfere with subsequent vacuum box testing. If, however,
pulling up on the extrudate squeeze-out pulls the entire extrudate
off the sheet it is obviously unacceptable. Squeeze-out generally
means that the extrusion die was not riding directly against the
geomembrane, the extrudate temperature was improper for adequate
flow, or the seaming rate was too slow.
Extrudate
Squeeze-Out
or Flashing
Figure 5.11. Schematic diagrams of various cross sections of
extrusion fillet seams.
39
-------
(1) Where possible, inspect the underside of the lower geomembrane for
heat distortion. This can be done at the end of seams and where
samples are cut out of the seam. If the underside is greatly
distorted, lower the temperature or increase the rate of seaming.
For thick HOPE geomembranes of 2 mm (80 mils) or greater there
should never be any indication of this type of thermal
"puckering". VLDPE seams which receive too much heat during
seaming will exhibit an increase in the amount of waves visible
along the length of the seam.
(m) If properly planned, each seam run should terminate at a panel
end, at a specific detail or on a long straight run where it can
be easily resumed.
(n) If the seaming needs to be interrupted at mid-seam, the extrudate
should end abruptly, with the extrudate being no thicker than in a
normal weld, rather than terminate with a large mass of solidified
extrudate.
(o) Where extrusion fillet welds are temporarily terminated long
enough to cool, they must be ground prior to applying new
extrudate over the existing seam. This restart procedure must
necessarily be followed on patches, pipes, fittings, appurtenances
and "T" or "Y" shaped seams.
(p) Depending upon the records to be kept, one might record a number
of different temperatures and/or the rate of seaming. This is a
site specific decision usually determined by the contract
specification or CQC/CQA Documents.
5.5 AFTER SEAMING
(a) A smooth insulating plate or heat insulating fabric is always to
be placed beneath the hot extrusion welding apparatus after usage.
The tip die and barrel must not be placed on any geomembrane or
other geosynthetic surface - it is extremely hot and can cause
severe damage.
(b) Visual inspection of the extrudate bead should be made
particularly for straight line alignment, height, and uniformity
of surface texture. There should be no bubbles or pock marks in
the extrudate. Such surface details on the extrudate indicates
the presence of air, water or debris within the extrudate rod or
pelletized polymer.
(c) Grind marks should only be visible for 0.6 cm (1/4 inch) beyond
the extrudate. They should be extremely faint and never appear as
heavy gouge marks, recall Figures 5.8 and 5.9. Excessive grinding
also has a depth consideration. As stated previously, excessive
is considered to be greater than 10% of the geomembrane thickness.
If it is excessive, it is not acceptable to apply additional
40
-------
extrudate over the original extrusion fillet seam. It is
necessary to place a cap strip over the entire seam where the
excessive grinding is observed.
(d) The seam must be checked visually for uniformity of width and
surface continuity. Usually the installer will use a vacuum box
to check for voids or gaps in the seam.
(e) When unbonded areas are located, they should be patched with at
least 15 cm (6 inches) of geomembrane extending on all sides.
(f) Any area of the geomembrane where puncture holes are observed must
be patched as above with at least 15 cm (6 inches) of geomembrane
extending beyond the affected areas.
(g) Photographs of various types of extrusion fillet seams follow in
Figure 5.12.
5.6 UNUSUAL CONDITIONS
This section is written to give insight into conditions which go beyond
the general description just presented.
(a) High winds, or gusts of wind, are always problematic for the liner
installation process. After deploying the geomembrane, the panels
or rolls must be adequately ballasted with sandbags. The actual
seam fabrication, however, will require the removal of some of the
sandbags leaving the windward edge vulnerable to wind uplift
forces. If possible, proper orientation of the overlap might be
helpful. Otherwise, additional labor must be on hand to only
remove sandbags immediately in front of the seaming operation.
The liner must be cleaned of any dirt and moisture left behind
after sandbag removal. They are then to be replaced behind the
completed seaming operation.
(b) Patches are necessary at locations where destructive test samples
are removed or where seams are shown to fail nondestructive
testing. These patches must extend a minimum of 15 cm (6 inches)
beyond the outer limits of the area to be repaired. For HOPE
liners the only method available is a hand held extrusion fillet
procedure as described in this section. Particular care must be
exercised when the end of the extrudate meets the beginning of the
circumferential patching run. The double heat that the polymer
will necessarily experience cannot be excessive, i.e., a large
mass of extrudate should not be visible at this location. For
VLDPE hot air seaming can be used to install patches.
(c) Details around sumps, pipes and other appurtenances for HOPE and
VLDPE liners are generally made by hand-held extrusion fillet
proedures as described in this section. They are perhaps the most
critical seams in a facility. Also due to their typical
41
-------
Figure 5.12. Photographs of cross sections of various types of HOPE
extrusion fillet seams.
Upper: Machine extrusion seam without squeeze-out.
Middle: Hand held extrusion seam without squeeze-out (note
thermal puckering at bottom at seam).
Lower: Hand held extrusion seam with squeeze-out.
42
-------
locations being at low points of the containment facility's
design, these areas inherently operate under larger hydraulic
heads. Should a defect from improper seaming occur in such a
location leakage rates and its associated adverse impacts are
heightened. Therefore, extreme care should be exercised in
ensuring seam integrity in these often difficult to reach
locations. The extrudate should be symmetric on both sheets to be
joined which is difficult for external and internal edges and
particularly at corners. The end of the seam run, where it joins
to the beginning, should be a smooth transition and not end with a
large mass of extrudate.
(d) This section was written for material temperatures that range
between 0°C (32°f) and 50°C (122°F), which is the temperature
range that is generally recognized as being acceptable for seaming
without taking special precautions. For sheet temperatures below
0°C (32°F) , shielding, pre-heating, and/or a slower seaming rate
may be required. More frequent seam testing and precautions to
prevent thawing subgrade may have to be taken. Sharp, frozen
subgrade should be avoided to eliminate point pressure damage
potential.
For sheet temperatures above 50°C (122°F), shielding and rate of
seaming should be adjusted. More frequent destructive seam
testing may have to be taken.
43
-------
FIELD NOTES:
44
-------
SECTION 6
DETAILS OF EXTRUSION FLAT SEAMS
As seen in Table 4.2, extrusion flat seaming is an applicable method for
the seaming HOPE and VLDPE geomembranes. Thus, this section is written
primarily for HOPE and VLDPE liners.
6.1 GEOMEMBRANE PREPARATION
(a) Note, that this document assumes that the proper geomembrane has
been visually inspected to ensure it is free of deep scratches, or
defects that would cause the sheet to not meet the specifications of
the installation. It is further assumed the sheet has been
delivered to the site and brought to its approximate plan position
for final installation and seaming. Only the material that can be
seamed that day should be deployed. All deployed material should be
adequately ballasted immediately to prevent wind uplift.
(b) The geomembrane, HOPE or VLDPE, will usually arrive on site in
rolls.
(c) The geomembrane should remain packaged or rolled and dry until ready
to use. The material should not be unrolled if the material
temperatures are lower than -10°C (14°F) due to the possibility of
cracking. If the panel is stored in a warm place, e.g. 10°C (50°F)
or above, prior to being unrolled on site, then it can be placed at
-18°C (0°F) or below temperatures providing the time between
removing the geomembrane from storage and deployment does not exceed
one-half working day.
(d) The two geomembrane sheets to be joined must be properly positioned
such that approximately 7.5 cm to 15.0 cm (3 to 6 inches) of overlap
exists.
(e) All personnel walking on the geomembrane should have smooth soled
shoes. Heavy equipment, e.g. pickups, tractors, etc., should not be
allowed on the geomembrane at any time, unless otherwise specified
by the manufacturer and approved in the CQC/CQA Documents.
(f) If the overlap is insufficient, lift the geomembrane sheet up to
allow air beneath it and "float" it into proper position. Avoid
dragging polyethylene geomembrane sheets particularly when they are
on rough soil subgrades since scratches in the material may create
various stress points of different depths and orientations.
45
-------
(g) If the overlap is excessive and is to be removed it should be done
by trimming the lower sheet only. If this is not possible and the
upper sheet must be trimmed do not use a knife with an unshielded
blade to cut off the excessive amount because the blade facing
downward can easily scratch the underlying geomembrane in a very
vulnerable location. A shielded blade or a hook blade should be
used to trim off the excess geomembrane. A photograph of such a
device is shown in Figure 6.1. Whenever possible it should be used
from beneath the liner in an upward cutting motion.
(h) All cutting and preparation of odd shaped sections or small fitted
pieces should be completed at least 15 m (50 ft.) ahead of the
seaming operation so that seaming may be continued with as few
interruptions as possible.
(i) Visually check the two opposing geomembrane sheets to be joined for
defects of sufficient magnitude to affect seam quality. The
criteria to be met and the procedures to be used in this regard
should be stipulated in the contract specifications and/or in the
CQC/CQA Documents.
(j) If the Plans require overlaps to be shingled in a particular
direction this should be checked.
(k) Excessive undulations (waves) along the seams during the seaming
operation should be avoided. When this occurs due to either the
upper or lower sheet having more slack than the other or because of
thermal expansion and contraction, it often leads to the undesirable
formation of "fishmouths" which must be trimmed, laid flat and
reseamed with a patch.
(1) There should be some slack in the installed liner which depends on
the type of geomembrane, the ambient and anticipated service
temperatures, length of time the geomembrane will be exposed,
location in the facility, etc. This is a design consideration and
the Plans and Specifications must be project specific on the amount
and orientation of slack.
(m) The sheets which are overlapped for seaming must be clean. If
dirty, they must be wiped clean with dry rags or other appropriate
materials.
(n) The sheets which are overlapped for seaming must be completely free
of moisture in the area of the seam. In the case of moisture air
blowers are usually preferred over rags for drying the membrane.
46
-------
Figure 6.1. Type of hook blade used in the cutting of liner materials.
(o) Seaming is not allowed during rain or snow, unless proper
precautions are made to allow the seam to be made on dry geomembrane
materials, e.g., within an enclosure or shelter.
(p) It is preferable not to have water-saturated soil beneath the
geomembrane during installation. Seaming boards help in this regard
by lifting the seams off the soil subgrade.
(q) If the soil beneath the geomembrane is frozen, the heat of seaming
can thaw the frost allowing water to be condensed onto the unbonded
region ahead of the seam being fabricated. This possibility may be
eliminated by the use of suitable seaming boards or slip sheets made
from excess pieces of geomembrane.
(r) The temperature of the geomembrane for seaming should be above
freezing, i.e. 0°C (32°F) unless it can be proven with a test strips
that good seams can be fabricated at lower temperatures. However,
temperature is less a concern to good seam quality than is moisture.
(s) For cold weather seaming, it may be advisable to preheat the sheets
with a hot air blower, to use a tent of some sort to prevent heat
losses during seaming and to make numerous test strips in order to
determine appropriate seaming conditions, e.g., equipment
temperatures may have to be set higher and/or seaming rates slowed
down during cold weather seaming.
47
-------
(t) Sheet temperatures for seaming should be below 50°C (122°F) as
measured by an infrared thermometer or surface contact thermocopule.
It is recognized that depending on material type and thickness,
higher temperatures may be allowed. It should also be recognized
that wind and cloud cover will determine the actual sheet
temperature. High temperatures affect not only worker performance
but will also affect durability of some geomembranes unless special
precautions, e.g. tents, etc., are taken. For temperatures above
this value special attention should be paid to the seaming
operation. Frequent test strips and more diligent nondestructive
testing is recommended.
NOTE: For items (q), (r), (s,) and (t) the CQC/CQA Documents and/or
project specifications and the regulatory requirements regarding hot
and cold temperature seaming limitations should be reviewed to avoid
possible problems with final construction certification acceptance.
6.2 EQUIPMENT PREPARATION
(a) Properly functioning portable electric generators must be available
within close proximity of the seaming region and with adequate
extension cords to complete the entire seam. These generators
should be of sufficient size or numbers to handle all seaming
electrical requirements. The generator must have rubber tires, or
be placed on a smooth plate such that it is completely stable so
that no damage can occur to the geomembrane or to the underlying
liner or subgrade material. Fuel (gasoline or diesel) for the
generator must be stored away from the geomembrane and if accidently
spilled on the geomembrane must be immediately removed. The area
should be inspected for damage to the geomembrane and repaired if
necessary.
(b) An electric rotary grinder having a grinding disk of approximately
10 cm (4 inch) in diameter and a sufficient quantity of #80 grit
paper must be available. Also acceptable is #100 grit paper which
is finer than #80. Sandpaper coarser than #80, e.g. #60, is not
acceptable. Grinding locations are shown in Figure 6.2. Caution
should be used to prevent overgrinding.
(c) Pressure rollers should be inspected for sharp edges or irregular
surfaces. On some systems these rollers are in tandem where the
front set (nearest the extrudate) should be adjusted to a lower
pressure than the rear set.
(d) All extrusion flat seaming devices must be equipped with properly
functioning temperature controllers displaying the temperature in
the extrusion barrel so that it may be monitored by seaming
personnel. It is recommended that the temperature of the extrudate
with an external thermocouple inserted into the melt stream be
periodically made to check the reading of the thermocouple
permanently mounted on the barrel. The CQC/CQA Documents should be
reviewed for appropriate temperature ranges.
48
-------
Grinding Areas
typ. 50 mm (2 in.)
ROTARY GRINDER
Grinding
•Area
typ. 50 mm (2 in.)
WIRE BRUSHING
Figure 6.2. Grinding locations and method used in the
preparation of extrusion flat seams.
(e) Adequate extrudate welding rods or pellets of appropriate dimension,
and of the same composition as the geomembrane itself, must be used.
They must be dry and clean to feed through the extruder. All
extrudate resin must be properly formulated so as to be the same
compound as the geomembrane sheet material. Manufacturers may be
required to provide a certification letter indicating that the
welding rod or pellets and the sheet are the same compound. If in
doubt, chemical fingerprinting methods must be performed, see
Reference 7. All extrudate material must be kept dry and free of
dirt, debris and foreign matter. When welding rod is used the size
must be consistent and appropriate for the seaming device.
6.3 TEST STRIPS
A general requirement of most CQA Documents is that "test seams" or "test
strips" be made on a periodic basis. Test strips generally reflect the quality
of field seams but should never be used solely for final field seam acceptance.
Final field seam acceptance should be specified in the contract specification
and should include a minimum level of destructive testing of the production
field seams. Test strips are made to minimize the amount of destructive
sampling/testing which requires subsequent repair of the final field seam.
Typically these test seams, for each seaming crew, are made about every four
hours, or every time equipment is changed, or if significant changes in
geomembrane temperature are observed, or as required in the contract
specification. This is a recommended practice that should be followed when
seaming all types of geomembranes. The purpose of these tests is to establish
that proper seaming materials, temperatures, pressures, rates, and techniques
along with the necessary geomembrane pre-seaming preparation is being
accomplished. Test strips may be used for CQA/CQC evaluation, archiving, for
exposure tests, etc., and must be of sufficient length to satisfy these various
needs.
49
-------
Each seaming crew and the materials they are using must be traceable and
identifiable to their test seams. While the test seams are being prepared,
cured, and CQC tested, the seaming crew may continue to work as long as the
seams they have made (and are making) since their last acceptable test sample
strip was prepared, are completely traceable and identifiable. If a test seam
fails to meet the field seam design specification, then an additional test seam
sample will have to be made by the same seaming crew - using the same tools,
equipment and seaming materials - and retested.
The liner's finished field seams will not be accepted unless the before
and after "test seam sample strip" CQC test results (or other CQC seam test
result criteria as required per the design specification) are acceptable per
the site's design specifications. If a seam is not accepted, destructive
testing of samples from the actual seam will be removed from the liner and
tested. If the actual seam destructive test results still do not meet the
design specification requirement, then the unacceptable seams will all have to
be repaired or reconstructed with seaming materials by a test proven seaming
crew that has passed its testing requirements. The procedure illustrated in
the flow chart of Figure 6.3 must be followed. Note that the failure of test
strip 1 requires two actions: (a) the making of test strip 2, and (b) an
increased frequency of destructive tests on production field seams made during
the curing of test strip 1 (if any were made). This increased frequency must
be stipulated in the contract specifications or in the CQC/CQA Documents.
If the destructive seams fail or if test strip 2 fails, production field
seaming is halted. All production field seams made during the interval are
repaired per the contract specifications or CQC/CQA Documents to the point of
previous acceptance with an approved seaming crew.
At this point, the seaming crew that failed to pass both strip tests must
adjust and recertify current seaming equipment and technique or obtain new
seaming equipment, tools and/or retrain personnel and begin making initial test
strip samples.
Test strips are prepared as shown in Figure 6.4. Figure 6.4(a) shows the
flat extrusion device from a side view and Figure 6.4(b) from a rear view. The
test strips are made on small sections of excess geomembrane in the identical
manner of making actual production seams. When they cool, they are cut into
sections and properly identified. For geomembranes that are seamed by
extrusion or thermal methods, the seams can be tested after they are allowed to
cool in ambient air at least 5-10 minutes prior to peel and shear testing.
50
-------
•Halt: Sttmlng Cnw filling la Pnptrt
Aeetpttalt Tttt Strlpt Mty Hta.uln
attn/nlng InAeeonltnet wtth CQC/CO4 Documtntt
Figure 6.3. Test strip process flow chart.
51
-------
Figure 6.4(a). Side view of an extrusion flat welding device showing
the extrudate feed arm between the overlapping
geomembrane sheets and the roller immediately behind.
52
-------
Figure 6.4(b). Rear view of the extrusion flat device as it
would appear at the completion of the seam.
53
-------
As previously stated, all seam test samples must be prepared in triplicate
sets from a single continuous test strip which can be cut in thirds; one set
for CQC tests, one set for CQA tests and one set made available to (or retained
for) the agency/owner/design organization. If referee test results are
required, CQA test results from destructive testing of actual seam samples will
prevail.
During the CQC and CQA test requirement periods, a liner should not be
covered and it cannot be placed into service. This will insure repairing or
reconstructing in the event it is required. During this period it is
imperative that the liner be properly ballasted and otherwise secured so as to
prevent wind or unusual weather damage.
6.4 ACTUAL SEAMING PROCESS
(a) Either by surface grinding, preheating air or preheating wedge, the
area to be seamed should now be ready to accept the extrudate in the
form of a ribbon placed between the two sheets.
(b) If grinding is required, the grinding of the lower sheet is to be
done first, with a suitable width (approximately 5.0 to 7.5 cm [2 to
3 inches]) being prepared such that surface oxide is removed and the
sheet is roughened. The depth of the grind marks must be no greater
than 10% of the original thickness of the sheet. Initial grinding
depths should be targeted to be less than 5% of the sheet thickness.
Areas where grinding depths are greater than 10% should not be
incorporated into the seam.
(c) The upper sheet is bent over backwards but not creased, so that its
underside can be ground at the location where it will meet the lower
sheet's prepared surface. It is important to note that all ground
sheet must eventually be covered with extrudate to within 0.6 cm
(1/4 inch).
(d) Alternatively to the type of surface preparation just described in
parts (b), and (d), an automated wire brush technique can be used.
With this instrument it is possible to prepare the bottom of the top
sheet and the top of the bottom sheet at the same time, see Figure
6.2. It should be noted that an even surface must be prepared. The
surfaces should be inspected for uniformity and grinding depths less
than or equal to 10% of the sheet thickness.
(e) If the flat extrusion device is equipped with pre-heating air or
pre-heating wedge preceding the extrudate, grinding of either type
just described is not necessary. It must be shown, however, by the
use of test strips that these techniques do, indeed, provide
adequate seam strength in shear and in peel testing.
54
-------
(f) Preheating of the opposing surfaces with hot air or hot wedge
devices must be applied to the full seam width at a constant
temperature. The nozzle, or wedge, should be inspected for
obstructions or scratches on a daily basis. Care should be taken in
choosing the nozzle design and magnitude of the air pressure. If
excessive air is discharged under the top geomembrane it could
create a backpressure that may blow dust and small soil particles
into the seam area.
(g) The extrusion welder is to be purged of all heat-degraded extrudate
in the barrel prior to beginning a seam. This must be done every
time the extruder is restarted after a 2 min., or longer, period of
inactivity. The purged extrudate should not be discharged onto the
surface of previously placed liner nor on the prepared subgrade
where it would eventually form a hard lump under the liner causing
stress concentrations and possibly premature failure.
(h) Some extrudate should also be ejected to see if the nozzle is the
appropriate width and thickness. Usually flat extrudate ribbons are
3.8 to 5.0 cm (1.5 in. to 2.0 in.) wide and about 1.5 mm (60 mils)
thick. However, welding speed will affect this thickness, which
ranges from about 0.5 mm (20 mils) thick when moving rapidly, to 2.0
mm (80 mils) thick when moving slowly. Properly functioning
temperature controllers must display the extrudate temperature. A
photograph and schematic diagram of a extrusion flat seaming device
is given in Figure 6.5.
(i) The extrudate is placed at about (250'C) 480*F in a full width, full
thickness ribbon, see Figure 6.6. It cannot be visually inspected
since it is occurring between the two sheets, directly following the
sheet preparation by grinding, preheating air or preheating wedge
and directly preceding the pressure rollers.
(j) The outside edge of the seam should be visually observed to ensure
that the extrudate is embedded between the liner sheets. Three
cases are possible. These are: 1) the edge of the extrudate being
somewhat under the overlapping sheet, 2) exactly even with it, or
3) beyond it in the form of "squeeze-out". Either one of the latter
two situations are necessary if vacuum box testing of the seam is
subsequently required.
(k) The rollers exert considerable pressure and are adjusted according
to sheet thickness. Indentations on the surface of the upper
geomembrane should be observable but should not create a rut, e.g.,
the indentation should be barely capable of being felt.
55
-------
I
_We|dinj Direction^
Contoct HOPE
j Pressure Extrudate TubeM)ie
With Hot Air Jets
Principles of Extrusion Welding For Site Joining
Figure 6.5. Photographs and schematic diagram of extrusion flat
seaming of geomembrane sheets.
56
-------
Extrudate
T
typ
k-*
-^ ».
. 25 mm tyP- 50 mm
1 in.) (2 in.)
Lower Geomembrane
S 3t
Figure 6.6. Schematic diagram of cross section of extrusion flat
seam with extrudate out to the edge of the upper
geomembrane.
(1) Thermal "puckering" of the upper surface of the overlying
geomembrane should not appear. Although the lower surface of the
underlying geomembrane is rarely able to be inspected (except at
sheet ends, trial strips, or where samples are taken) it should not
be puckered. Thermal puckering signifies excessive heat and/or
insufficient seaming rate.
(m) Depending upon the records to be kept, one might record a number of
different temperatures and/or the rate of seaming. This is a site
specific decision usually determined by the contract specification
or CQC/CQA Documents.
(n) It is necessary that the operator keep constant visual contact with
the temperature controls, as well as the completed seam coming out
of the machine. Occasional adjustments of temperature or speed as
the result of changing ambient conditions will be necessary to
maintain a consistent seam. Constant visual and hands on inspection
is also recommended. If changes in the welding conditions are made
as a response to a changing welding environment, an additional
destructive sample test should be performed shortly after the change
is made.
6.5 AFTER SEAMING
(a) Hand-held grinders or mechanical wire brushes are always to be
turned off when not in use. If placed on the geomembrane while
running, they can cause considerable damage.
(b) A smooth insulating plate or heat insulating fabric is to be placed
beneath any hot welding apparatus after usage.
57
-------
I
(c) Grinding marks on the lower sheet of the completed seam should be
observable but only for a distance of 0.6 cm (1/4 inch) beyond the
extrudate. Note, however, that only the lower sheet can be
inspected in this regard.
(d) If properly planned, each seam run should terminate at a panel end,
specific detail or on a long straight run where it can be easily
resumed.
(e) Where extrusion flat welds are terminated long enough to cool, the
start-up continuation seam must completely melt the leading edge of
the cooled seam. Since this is occurring beneath the overlapped
sheet and cannot be observed, the location must be marked for
subsequent vacuum box testing. If it fails, the area must be
repaired or reconstructed.
(f) The extrudate end should trail off gradually, rather than terminate
with a large mass of solidified extrudate.
(g) The seam must be checked visually for uniformity of width and
surface continuity. Usually the installer will use a vacuum box to
check for voids or gaps in the seam.
(h) When unbonded areas are located, they should be patched with at
least 15 cm (6 inches) of geomembrane extending on all sides. Any
area of the geomembrane where puncture holes are observed must be
patched as above with at least 15 cm (6 inches) of geomembrane
extending beyond the affected areas. If grinding is to be performed
to prepare the geomembrane, review instructions provided in Section
5.
(i) Photographs of the various types of extrusion flat seams are shown
in Figure 6.7.
6.6 UNUSUAL CONDITIONS
This section is written to give insight into conditions which go beyond
the general description just presented.
(a) High winds, or gusts of wind, are always problematic for liners.
After deploying the geomembrane, the panels must be adequately
ballasted with sandbags. The actual seam fabrication, however, will
require the removal of some of the sandbags leaving the windward
edge vulnerable to wind uplift forces. If possible, proper
orientation of the overlap might be helpful. Otherwise, additional
labor must be on hand to only remove sandbags immediately in front
of the seaming operation. The liner must be cleaned of any dirt and
moisture left behind after sandbag removal. They are then to be
replaced behind the completed seaming operation.
58
-------
Figure 6.7. Photographs of cross sections of HOPE extrusion flat
seams.
Upper: Extrudate short of edge of overlapping sheet.
Middle: Extrudate exactly at the edge- of overlapping
sheet.
Lower: Extrudate squeeze-out beyond the edge of
overlapping sheet-.
59
-------
(b) Patches are necessary at locations where destructive test samples
are removed or where seams are shown to fail nondestructive testing.
These patches must extend a minimum of 15 cm (6 inches) beyond the
outer limits of the area to be repaired. For HOPE liners the only
method available is a hand held extrusion fillet procedure as
described in Section 5. Particular care must be exercised when the
end of the extrudate meets the beginning of the run. The double
heat that the polymer will necessarily experience cannot be
excessive, i.e., a large mass of extrudate should not be visible at
this location.
(c) Details around sumps, pipes and other appurtenances for HOPE and
VLDPE liners must necessarily be made by hand-held extrusion fillet
procedures as described in Section 5. They are perhaps the most
demanding seams in a facility. Also due to their typical locations
being at low points of the containment facility's design, these
areas inherently operate under larger hydraulic heads. Should a
defect from improper seaming occur in such a location leakage rates
and its associated adverse impacts are heightened. Therefore,
extreme care should be exercised in ensuring seam integrity in these
often difficult to reach locations. The extrudate should be
symmetrical on both sheets to be joined which is difficult for
external and internal edges and particularly at corners. The end of
the seam run, where it joins to the beginning, should be a smooth
transition and not end with a large mass of extrudate.
(d) This section was written for material temperatures that range
between (0°C) 32°F and (50°C) 122°F. This is the temperature range
that is generally recognized as being acceptable for seaming without
taking special precautions.
For sheet temperatures below 0°C (32"F), shielding, preheating,
and/or a slower seaming rate may be required. More frequent seam
testing and precautions to prevent thawing subgrade (previously
discussed) may have to be taken. Sharp, frozen subgrade should be
avoided to eliminate point pressure damage potential.
For sheet temperatures above 50'C (122°F), shielding and rate of
seaming should be adjusted. More frequent destructive seam testing
may have to be taken.
60
-------
FIELD NOTES:
61
-------
FIELD NOTES:
I
62
-------
SECTION 7
DETAILS OF HOT WEDGE SEAMS
As seen in Table 4.2, hot wedge seaming is an applicable method for the
seaming all thermoplastic geomembranes.
7.1 GEOMEMBRANE PREPARATION
(a) Note, that this document assumes that the proper geomembrane has
been visually inspected to ensure it is free of deep scratches,
or defects that would cause the sheet to not meet the
specifications of the installation. It is further assumed the
sheet has been delivered to the site and brought to its
approximate plan position for final installation and seaming.
Only the material that can be seamed that day should be deployed.
All deployed material should be ballasted as required to prevent
wind uplift.
(b) If the geomembrane is CPE, CPE-R, CSPE-R, EIA, EIA-R, PVC or
PVC-R it will usually arrive on site in the form of fabricated
panels which are accordion-folded in both directions. They are
generally packaged in palletized, heavy cardboard containers. If
the geomembrane is HOPE or VLDPE, it will arrive on the site in
rolls.
(c) The geomembrane should remain packaged or rolled and dry until
ready to use. The material should not be unfolded or unrolled if
the material temperatures are lower than -10"C (14"F) due to the
possibility of cracking. If the panel is stored in a warm place,
e.g. 10°C (50'F) or above, prior to being unfolded or unrolled on
site, then it can be placed at -18'C (O'F) or below temperatures
providing the time between removing the geomembrane from storage
and deployment does not exceed one-half working day. Geomembrane
deployment may be allowed under other conditions but the CQC/CQA
Documents and/or project specifications must be specific as to
the conditions.
(d) The two geomembrane sheets to be joined must be properly
positioned such that approximately 7.5 cm to 15.0 cm (3 to 6
inches) of overlap exists. All personnel walking on the
geomembrane should have smooth soled shoes. Heavy equipment,
e.g. pickups, tractors, etc., should not be allowed on the
geomembrane at any time, unless otherwise specified by the
manufacturer and approved in the CQC/CQA Documents.
63
-------
(e) If the overlap is insufficient and it does not fully cover the
wedge, lift the geomembrane up to allow air beneath it and
"float" it into proper position. Avoid dragging geomembrane
sheets made from HOPE particularly when they are on rough soil
subgrades since scratches in the material create stress points of
different depths and orientations.
(f) When most reinforced geomembranes are cut to accommodate odd
shapes or to fit small pieces, resealing of the exposed scrim by
flood coating is required by the use of the manufacturer's or
fabricator's approved liquid sealant.
(g) If the overlap is excessive when placing HOPE and VLDPE and is to
be removed, it should be done by trimming the lower sheet. If
this is not possible and the upper sheet must be trimmed, do not
use a knife with an unshielded blade to cut off the excessive
amount because the blade facing downward can easily scratch the
underlying geomembrane in a very vulnerable location. A shielded
blade or a hook blade should be used to trim off the excess
geomembrane. A photograph of such a device is shown in Figure
7.1. Whenever possible it should be used from beneath the liner
in an upward cutting motion. For liners made from CPE, CPE-R,
CSPE-R, EIA, EIA-R, PVC, PVC-R and VLDPE the excess material can
be cut by a scissor or can be worked away from the edges of the
seam to maintain proper overlap.
(h) All cutting and preparation of odd shaped sections or small
fitted pieces should be completed at least 15 m (50 ft.) ahead of
the seaming operation so that seaming can be completed with as
few interruptions as possible.
(i) The two opposing sheets to be joined should be visually checked
for defects of sufficient magnitude to affect seam quality. The
criteria to be met and the procedures to be used in this regard
should be stipulated in the contract specifications and/or in the
CQC/CQA Documents.
(j) If the construction plans require overlaps to be shingled in a
particular direction this should be checked.
(k) Excessive undulations (waves) along the seams during the seaming
operation should be avoided. When this occurs due to either the
upper or lower sheet having more slack than the other or because
of thermal expansion and contraction, it often leads to the
undesirable formation of "fishmouths" which must be trimmed, laid
flat and reseamed with a patch.
64
-------
Figure 7.1. Type of hook blade used in the cutting of liner materials.
(1) For all liners, there should be some slack in the installed liner
which depends on the type of geomembrane, ambient and anticipated
service temperatures, length of time the geomembrane will be
exposed, location in the facility, etc. This is a design
consideration and the Plans and Specifications must be project
specific on the amount and orientation of slack.
(m) The sheets which are overlapped for seaming must be clean. If
dirty, they must be cleaned with dry rags or other appropriate
materials.
(n) The sheets which are overlapped for seaming must be free of
moisture in the area of the seam.
(o) Seaming is not allowed during rain or snow, unless proper
precautions are made to allow the seam to be made with dry
geomembrane materials, e.g., within an enclosure or shelter.
(p) It is preferable not to have water saturated soil beneath the
geomembrane during installation. Seaming boards help in this
regard by lifting the seams off the soil subgrade.
(q) If the soil beneath the geomembrane is frozen, the heat from hot
air seaming devices or any preheating lamps that may be used can
thaw the frost allowing water to be condensed onto the unbonded
65
-------
region ahead of the seam being fabricated. This possibility may
be eliminated by the use of suitable seaming boards or slip
sheets made of excess geomembrane material.
(r) Ambient temperatures for seaming should be above freezing, i.e.,
0*C (32*F) unless it can be proven with test strips that good
seams can be fabricated at lower temperatures. However,
temperature is less a concern to good seam quality than is
moisture.
(s) For cold weather seaming, it may be advisable to preheat the
sheets with a radiant heater or a blower, to use a tent of some
sort to prevent heat losses during seaming and to make numerous
test strips in order to determine appropriate seaming conditions,
e.g., equipment temperatures may have to be set higher and/or
seaming rates slowed down during cold weather seaming.
(t) Sheet temperatures for seaming should be below 50'C (122*F) as
measured by an infrared thermometer or surface contact
thermocouple. It is recognized that depending on material type
and thickness, higher temperatures may be allowed. It should
also be recognized that wind and cloud cover will determine the
actual sheet temperature. High temperatures affect not only
worker performance but may also affect seam durability of some
geomembranes unless special precautions are taken. For
temperatures above this value, frequent test strips and more
diligent nondestructive testing is recommended.
NOTE: For items (q), (r), (s,) and (t) the CQC/CQA Documents
and/or project specifications and the regulatory requirements
regarding hot and cold temperature seaming limitations should be
reviewed to avoid possible problems with final construction
certification acceptance.
7.2 EQUIPMENT PREPARATION
(a) Properly functioning portable electric generators must be
available within close proximity of the seaming region and with
adequate extension cords to complete the entire seam. These
generators should be of sufficient size or numbers to handle all
seaming electrical requirements. The generator must have rubber
tires, or be placed on a smooth plate such that it is completely
stable so that it cannot damage the geomembrane or to the
underlying clay liner or subgrade material. Fuel (gasoline or
diesel) for the generator must be stored away from the
geomembrane, and if accidently spilled on the geomembrane it must
be immediately removed. The areas should be inspected for damage
to the geomembrane and repaired if necessary.
66
-------
(b) Hot wedge seaming devices are completely self contained systems
sometimes referred to as a "mouse" or "hot shoe". Photographs of
different types of hot wedge seaming devices are shown in
Figure 7.2.
(c) As the hot wedge method is one of melting the opposing surfaces
of the two sheets to be joined, no grinding of sheets is
necessary, nor allowed.
(d) Hot air tacking of the geomembrane sheets as done in extrusion
fillet seaming is not possible since the wedge must travel
between opposing parallel sheets which are to be joined.
(e) The hot wedge itself, or "anvil", should be inspected to see that
it is uniform and uniformly tapered. Various typ^s are currently
available. Some are smooth surfaced while others have patterned
ridges in the direction of the seam or at a slight angle. The
taper dimensions vary according to different types of machines.
The major point for inspection is that no sharp edges should
exist wherever the wedge meets geomembrane sheet surfaces.
(f) A single hot wedge has an anvil which is uniform over its entire
surface. A dual wedge has a split anvil forming two separate
tracks, see the sketches of Figure 7.3. If a dual, or split, hot
wedge seam is being made, the recessed space for the central
unseamed portion should be examined to ensure the cavity is
clean.
(g) Knurled rollers are used for applying pressure on the sheets and
driving the device. They immediately follow the pointed end of
the anvil. The knurled rollers should be inspected to ensure
there are no sharp surfaces and that wheels are smoothly beveled
on the edges.
(h) If a chain drive powers the device and applies pressure to the
nip/drive rollers it should be inspected for synchronization of
travel, proper functioning and fit. Loose chains or damaged
sprockets should be repaired or replaced.
(i) As the geomembrane sheet materials pass through the machine, they
must come in contact with the full width of the wedge in order to
heat the material uniformly. Idler rollers or similar devices,
on both sides of the wedge are adjustable and must make the
material conform to the wedge as it passes through the machine.
The procedure for doing this with some equipment is as follows:
Insert the lower and upper layers of geomembrane material in the
nip/drive rollers, which will change the wedge height between the
idler rollers. Then, lock the wedge in position, and adjust the
idlers so that one layer fits snugly between the wedge and the
idlers. The wedge has an adjustment that is actually a stopping
device to keep the wedge from being pulled into the nip/drive
rollers. Caution must be taken to ensure that the wedge is not
67
-------
Figure 7.2. Various types of hot wedge seaming devices.
68
-------
typ. tl
25 mm
(1 in.)
typ. 75 mm (3 in.) I
Single Hot Wedge
typ. 25-75 mm
(1-3 in.)
typ. 75 mm (3 in.)
Dual (Split) Hot Wedge
Figure 7.3. Diagrams of the hot wedge elements (i.e., the anvil)
upon which the two sheets to be joined are passed.
adjusted too closely to the nip/drive rollers, especially when
material is not going through the machine. The drive, or wedge
units, must be disengaged before the material runs completely out
of the machine. Serious damage will occur to the geomembrane
sheets if the wedge gets pulled through the nip/drive rollers.
Please note that there are automatically adjusting machines in
use. These machines automatically adjust the position of the
geomembrane with respect to the roller drive mechanism. For this
reason the above and remaining instructions should be
appropriately modified.
(j) The front part of the seaming device should be inspected for
sharp corners and irregular details which may damage the
geomembranes.
(k) Temperature controllers on the wedge device should be set
according to type of geomembrane, thickness, ambient temperature,
rate of seaming, and location of thermocouple within the device.
Temperature gages should be checked for accuracy and
repeatability. Table 7.1 gives typical values but this is a
site, material and device specific decision usually determined by
CQC/CQA Documents or site specific conditions.
(1) If available, the force sensors at the nip rollers should be
checked for accuracy and repeatability.
69
-------
TABLE 7.1. TEMPERATURE RANGES FOR HOT WEDGE SEAMING OF THERMOPLASTIC
GEOMEMBRANES (TEMPERATURES ARE WITHIN THE WEDGE ITSELF).
Geomembrane Type
CPE
CPE-R
CSPE-R
EIA
EIA-R
HOPE***
PVC
PVC-R
VLDPE***
Minimum *
•C CF)
170 (340)
170 (340)
180 (360)
155 (310)
155 (310)
315 (600)
165 (330)
165 (330)
270 (520)
Maximum **
*C CF)
370 (700)
370 (700)
370 (700)
175 (345)
175 (345)
455 (850)
370 (700)
370 (700)
400 (750)
* For dry, warm weather seaming conditions
** For damp, cold weather seaming conditions
*** For textured or roughened HOPE or VLDPE sheet increase temperatures
about 25'C (45°F). Also slower seaming rates and higher pressures
may be required.
70
-------
7.3 TEST STRIPS
A general requirement of most CQA Documents is that "test seams" or
"test strips" be made on a periodic basis. Test strips generally reflect
the quality of field seams but should never be used solely for final field
seam acceptance. Final field seam acceptance should be specified in the
contract specification and should include a minimum level of destructive
testing of the production field seams. Test strips are made to minimize the
amount of destructive sampling/testing which requires subsequent repair of
the final field seam. Typically these test seams, for each seaming crew,
are made about every four hours, or every time equipment is changed, or if
significant changes in geomembrane temperature are observed or, as required
in the contract specification. This is a recommended practice that should
be followed when seaming all types of geomembranes. The purpose of these
tests is to establish that proper seaming materials, temperatures,
pressures, rates, and techniques along with the necessary geomembrane
pre-seaming preparation is being accomplished. Test strips may be used for
CQA/CQC evaluation, archiving, for exposure tests, etc., and must be of
sufficient length to satisfy these various needs.
Each seaming crew and the materials they are using must be traceable
and identifiable to their test seams. While the test seams are being
prepared, cured, and CQC tested, the seaming crew may continue to work as
long as the seams they have made (and are making) since their last
acceptable test sample strip was prepared, are completely traceable and
identifiable. If a test seam fails to meet the field seam design
specification, then an additional test seam sample will have to be made by
the same seaming crew - using the same tools, equipment and seaming
materials - and retested.
The liner's finished field seams will not be accepted unless the before
and after "test seam sample strip" CQC test results (or other CQC seam test
result criteria as required per the design specification) are acceptable per
the site's design specifications. If a seam is not accepted, destructive
testing of samples from the actual seam will be removed from the liner and
tested. If the actual seam destructive test results still do not meet the
design specification requirement, then the unacceptable seams will all have
to be repaired or reconstructed with seaming materials by a test proven
seaming crew that has passed its testing requirements. The procedure
illustrated in the flow chart of Figure 7.4 must be followed. Note that the
failure of test strip 1 requires two actions: (a) the making of test strip
2, and (b) an increased frequency of destructive tests on production field
seams made during the curing of test strip 1 (if any were made). This
increased frequency must be stipulated in the contract specifications or in
the CQC/CQA Documents.
If the destructive seams fail or if test strip 2 fails, production
field seaming is halted. All production field seams made during the
interval are repaired per the contract specifications or CQC/CQA Documents
to the point of previous acceptance with an approved seaming crew.
71
-------
•Holt: Sttmlng Cnw filling to frt/m
Acctpttblt Tttt Stript MtyRtquIn
RttrtlnlnglnAccanitnct HH/I CQC/COA Deamntt
Figure 7.4. Test strip process flow chart.
72
-------
At this point, the seaming crew that failed to pass both strip tests
must adjust and recertify current seaming equipment and technique or obtain
new seaming equipment, tools and/or retrain personnel and begin making
initial test strip samples.
For hot wedge seams test strips of the type shown in Figure 7.5(a-d)
are prepared. The seam is centered lengthwise between the two sheets to be
joined. Figure 7.5(a) shows the two geomembrane pieces to be seamed being
cleaned and properly aligned, 7.5(b) shows the actual test strip being
seamed, 7.5(c) shows the sampling of the test strip for subsequent
destructive testing, and 7.5(d) shows the individual samples cut from the
test strip being identified. For geomembranes that are seamed by thermal
methods, the seams can be tested after they are allowed to cool in ambient
air at least 5-10 minutes prior to shear and pael testing.
As previously stated, all seam test samples must be prepared in
triplicate sets preferably in a continuous seam which can be cut in thirds;
one set for CQC tests, one set for CQA tests and one set made available to
(or retained for) the agency/owner/design organization. If referee test
results are required, CQA test results from destructive tasting of actual
seam samples will prevail.
During the CQC and CQA test requirement periods, a liner should not be
covered and it cannot be placed into service. This will insure the ease and
viability of repairing or reconstructing in the event it is required.
During this period it is imperative that the liner be properly ballasted and
otherwise secured so as to prevent wind or unusual weather damage.
7.4 ACTUAL SEAMING PROCESS
(a) The hot wedge system (i.e., the "mouse" or "hot shoe") should be
properly positioned for the making of the desired single or dual
(split) seam.
(b) The principle of the hot wedge is that both surfaces to be joined
come into intimate contact with the hot wedge, or anvil. The
anvil slides between both layers of geomembranes and fusion is
brought about by compressing the two melted surfaces together,
causing an intermingling of the polymers from both sheets. The
hot anvil itself melts the surface of the viscous polymer sheets
and acts as a scraper/mixer, followed closely by the nip rollers
which squeeze the two geomembranes intimately together, see
Figure 7.6 for details.
73
-------
Figure 7.5(a). Two sheets of liner being cleaned and
prepared for trial seaming.
Figure 7.5(b). The two sheets being seamed together thereby
forming the test strip.
74
-------
Figure 7.5(c). The completed test strip being cut into individual samples
for subsequent inspection and destructive testing.
Figure 7.5(d). Marking the test strip samples for identification
and records.
75
-------
Joined
Geomembranej
Hot Wedge
Direction of Travel
Figure 7.6. Details of the hot wedge system showing relative positions
of the hot wedge, rollers and sheets to be joined.
76
-------
(c) The type of geomembrane, rate of seaming, and ambient factors
such as clouds, wind, and hot sun require the temperature setting
of the wedge to vary. Depending upon the records to be kept,
one might record a number of different temperatures. For
example, the temperature of the hot wedge, the temperature of the
sheet after seaming, the temperature of the sheet away from the
seaming area and the ambient temperature. This is a site
specific decision usually determined by the contract
specification or CQC/CQA Documents.
(d) Power for the drive motor should be off when positioning the
machine to make a seam. Manually place the machine within the
overlapped sheet of material. The sheets shall be guided between
the idlers and the wedge, and into the drive/nip rollers. This
procedure is only possible when starting with two new sheets.
When starting a weld in the middle of two sheets, the material
must be loaded from the sides. The machine is to be picked up a
few inches, loading the bottom sheet first, and then the top
sheet. As soon as the nip rollers are engaged and the wedge is
in position, the power to the drive motor should be turned on.
Once the sheets are between the nip rollers, they shall be
engaged immediately, otherwise a melt-through will occur within a
few seconds. The hot wedge should be moved into position and
locked.
(e) It is necessary that the operator keep constant visual contact
with the temperature controls, as well as the completed seam
coming out of the machine. Occasional adjustments of temperature
or speed as the result of changing ambient conditions will be
necessary to maintain a consistent seam. Constant visual and
hands on inspection is also recommended. If changes in the
welding conditions are made as a response to a changing welding
environment, the testing of an additional destructive sample
shortly after the change is recommended.
(f) On some soils, the device may "bulldoze" into the ground as it
travels. This causes soil to enter the seam area, making the
seam weak and unacceptable. To overcome this, it is recommended
that the operator take some of the weight off of the front of the
machine by lifting it slightly. Alternatively, some type of base
for the machine to travel on should be provided. Strips of
geotextile or geomembrane have proven effective to prevent this
bulldozing effect. Depending on the soil conditions it may be
necessary to change the size of the rollers in loose soils. It
is necessary that at least two people work together in making hot
wedge seams; one operator and one helper.
(g) A fully leak-proof T-connection is necessary wherever
intersecting seams are to be joined together. At such locations,
the hot wedge device must be removed a short distance
(approximately 15 cm or 6 inches) from the intersecting seam.
77
-------
For HOPE and VLDPE this short distance must be completed by
extrusion fillet seaming, see Figure 7.7. Note that the unbonded
free overlaps of the sheets are to be cut away to expose the edge
of the outside of the hot wedge seam. The surface must be ground
to remove the surface oxide, see Section 5. The extrudate bead
is then placed in a continuous fashion so as to provide complete
coverage of all areas not completed by the hot wedge device.
(h) For a leak proof T-connection in PVC, CSPE, CPE and EIA
materials, the short distance referred to in (g) above must be
completed by chemical bonding (fusion) or chemical adhesive.
7.5 AFTER SEAMING
(a) A smooth insulating plate or heat insulating fabric is to be
placed beneath the hot welding apparatus after usage.
(b) For HOPE and VLDPE a slight amount of "squeeze-out" or "flashing"
is a good indicator that the proper temperatures were achieved,
see the sketch of Figure 7.8. It signifies a proper seam in that
some of the melted polymer was laterally squeezed out of the seam
zone. If an excessive amount of hot melt is being squeezed out,
it is an indication of either too much heat, too much pressure,
or too slow a seaming rate. Reduce the temperature and/or
pressure and/or adjust the rate to correct the situation.
(c) For VLDPE liners of 1.0 mm (40 mils) thickness a long, low
wavelength pattern in the direction of the seam along its top
surface is indicative of a proper weld. If the wave peaks become
too close together, the machine speed should be increased until a
satisfactory pattern is present. The absence of this wavelength
pattern indicates that the machine speed should be decreased.
There will be no wavy pattern for VLDPE liners greater than 1.0
mm (40 mils) in thickness due to the inherent stiffness of the
thicker material.
(d) Nip/drive roller marks may show on the surface when using knurled
rollers. Their depth should be visually observable, but care
should be taken to insure that the nip drive rollers do not
create a rut, e.g. the indentation should be barely capable of
being felt.
(e) The hot wedge device has only a few adjustments that can be made,
but it is very important that they be checked regularly.
Cleaning of the machine should be done at least daily.
(f) The seam must be checked visually for uniformity of width and
surface continuity. Usually the installer will use a vacuum box
or "air lance" depending on the geomembrane material to check for
voids or gaps in the seam. For dual wedge seams the air channel
can be used to evaluate seam integrity.
78
-------
Extrudate
-^'f
Extrudate
Hot Shoe
»Fusion Weld
SECTION
r
fillet extrusion bead
Figure 7.7. Hot wedge T-seam detail.
79
-------
Upper Geomembrane
^Squeeze-Out" or
"Flashing"
typ. 12 mm
(0.5 in.)
typ. 12 mm
(0.5 in.)
typ. 12 mm
(0.5 in.)
Lower Geomembranf
Cross Section of Dual (Split)
Hot Wedge Seam
Figure 7.8. Schematic diagram of cross section of dual (split)
hot wedge seam illustrating squeeze-out.
(g) When unbonded areas are located they should be patched with at
least 15 cm (6 inches) of geomembrane extending on all sides.
Any area of the geomembrane where puncture holes are observed
they must be patched as above with at least 15 cm (6 inches) of
geomembrane extending beyond the affected areas. If grinding is
to be performed to prepare the geomembrane, review instructions
provided in Section 5.
(h) Photographs of cross sections of different types of hot wedge
seams follow in Figure 7.9.
7.6 UNUSUAL CONDITIONS
This section is written to give insight into conditions which go beyond
the general description just presented.
(a) High winds, or gusts of wind, are always problematic for liners.
After placing the geomembrane, the panels or rolls must be
adequately ballasted, e.g., with sandbags. The actual seam
fabrication, however, may require the removal of some of the
sandbags leaving the windward edge vulnerable to wind uplift
forces. If possible, proper orientation of the overlap might be
helpful. Otherwise, additional labor may be required to remove
sandbags immediately in front of the seaming operation. The
liner must be cleaned of any dirt and moisture left behind after
sandbag removal. They are then to be replaced behind the
completed seaming operation.
80
-------
Figure 7.9. Photographs of cross sections of HOPE hot wedge seams.
Upper: Single hot wedge seam with acceptable
squeeze-out
Middle: Dual hot wedge seam with excessive squeeze-out
Lower: Dual hot wedge seam with acceptable squeeze-out
81
-------
(b) Patches are necessary at locations where destructive test samples
are removed or where seams are shown to fail nondestructive
testing. These patches must extend a minimum of 15 cm (6 inches)
beyond the outer limits of the area to be repaired. For HOPE
liners the only method available is a hand held extrusion fillet
procedure as described in Section 5. Particular care must be
exercised when the end of the extrudate meets the beginning of
the run. The double heat that the polymer will necessarily
experience cannot be excessive, i.e., a large mass of extrudate
should not be visible at this location. For other geomembrane
types, one or more of the following methods may be used; hot air,
chemical or adhesive. These will be described in subsequent
sections.
(c) Details around sumps, pipes and other appurtenances are perhaps
the most demanding seams in a facility. Also due to their
typical locations being at low points of the containment
facility's design, these areas inherently operate under larger
hydraulic heads. Should a defect from improper seaming occur in
such a location leakage rates and its associated adverse impacts
are heightened. Therefore, extreme care should be exercised in
ensuring seam integrity in these often difficult to reach
locations. For HOPE and VLDPE the extrudate should be symmetric
on both liners to be joined which is difficult for external and
internal edges and particularly at corners. The end of the seam
run, where it joins to the beginning, should be a smooth
transition and not end with a large mass of extrudate. For HOPE
and VLDPE liners these details must necessarily be made by hand-
held extrusion fillet procedures as described in Section 5. For
PVC, CSPE, EIA and CPE type geomembranes, either hot air,
chemical or adhesive methods may be used.
(d) This section was written for material temperatures that range
between O'C (32°F) and 50°C (122'F). This is the temperature
range that is generally recognized as being acceptable for
seaming without taking special precautions.
For sheet temperatures below 0"C (32*F), shielding, preheating,
and/or a slower seaming rate may be required. More frequent seam
testing and precautions to prevent thawing subgrade (previously
discussed) may have to be taken. Sharp, frozen subgrade should
be avoided to eliminate point pressure damage potential.
For sheet temperatures above 50°C (122'F), shielding and rate of
seaming should be adjusted. More frequent destructive seam
testing may have to be taken.
82
-------
FIELD NOTES:
83
-------
FIELD NOTES:
84
-------
SECTION 8
DETAILS OF HOT AIR SEAMS
Hot air seams represent an applicable seaming method for all geomembranes
listed in Table 4.2.
8.1 GEOMEMBRANE PREPARATION
(a) Note, that this document assumes that the proper geomembrane has
been visually inspected to ensure it is free of deep scratches, or
defects that would cause the sheet to not meet specifications of the
installation. It is further assumed the sheet has been delivered to
the site and brought to its approximate plan position for final
installation and seaming. Only the material that can be seamed that
day should be deployed. All deployed material should be ballasted
as required to prevent wind uplift.
(b) If the geomembrane is CPE, CPE-R, CSPE-R, EIA, EIA-R, PVC, or
PVC-R and in some cases VLPDE, it will usually arrive on site in the
form of fabricated panels which are accordion-folded in both
directions. They are generally packaged in palletized, heavy
cardboard containers. If the geomembrane is VLDPE (generally) or
HOPE, it will arrive on the site in rolls.
(c) The geomembrane should remain packaged or rolled and dry until ready
for use. The material should not be unfolded or unrolled if the
material temperatures are lower than -10°C (14°F) due to the
possibility of cracking. If the liner is stored in a warm place,
e.g. 10"C (50°F) or above, prior to being unfolded or unrolled on
site, then it can be placed at -18°C (O'F) or below temperatures
providing the time between removing the geomembrane from storage and
deployment does not exceed one-half working day. Geomembrane
deployment may be allowed under other conditions but the CQC/CQA
Documents and/or project specifications must be specific as to the
conditions.
(d) The two geomembrane sheets to be joined must be properly positioned
such that approximately 7.5 cm to 15.0 cm (3 to 6 inches) of overlap
exists. All personnel walking on the geomembrane should have smooth
soled shoes. Heavy equipment, e.g. pickups, tractors, etc. should
not be allowed on the geomembrane at any time, unless otherwise
specified by the manufacturer and approved in the CQC/CQA Documents.
85
-------
(e) If the overlap is insufficient and it does not fully cover the air
flow nozzle, lift the sheet up to allow air beneath it and "float"
it into proper position. Avoid dragging geomembrane sheets made
from HOPE particularly when they are on rough soil subgrades since
scratches in the material may create various stress points of
different depths and orientations.
(f) When most reinforced geomembranes are cut to accommodate odd shapes
or to fit small pieces, resealing of the exposed scrim by flood
coating is required by the use of manufacturer's or fabricator's
approved liquid sealant.
(g) If the overlap is excessive when placing HOPE and VLDPE and is to be
removed, it should be done by trimming the lower sheet. If this is
not possible and the upper sheet must be trimmed, do not use a knife
with an unshielded blade to cut off the excessive amount because the
blade facing downward can easily scratch or cut into the underlying
geomembrane in a very vulnerable location. A shielded blade or a
hook blade should be used to trim off the excess geomembrane. A
photograph of such a device is shown in Figure 8.1. Whenever
possible it should be used from beneath the liner in an upward
cutting motion. For liners made from CPE, CPE-R, CSPE-R, EIA, EIA-
R, PVC or PVC-R and VLDPE the excess material can be cut by
scissors, see Figure 8.2 or can be worked away from the edges of the
seam to maintain proper overlap.
(h) All cutting and preparation of odd shaped sections or small fitted
pieces should be accomplished at least 15 m (50 ft.) ahead of the
seaming operation so that seaming can be completed with as few
interruptions as possible.
(i) The two opposing geomembrane sheets to be joined should visually be
checked for defects of sufficient magnitude to affect seam quality.
The criteria to be met and the procedures to be used in this regard
should be stipulated in the contract specifications and/or in the
CQC/CQA Documents.
(j) If the construction plans require overlaps to be shingled in a
particular direction this should be adhered to and verified.
(k) Excessive undulations (waves) along the seams during the seaming
operation should be avoided. When this occurs due to either the
upper or lower sheet having more slack than the other or because of
thermal expansion and contraction, it often leads to the undesirable
formation of "fishmouths" which must be trimmed, laid flat and
reseamed with a patch. An example of a fishmouth and its correction
is shown in Figure 8.3(a-d).
86
-------
Figure 8.1.
Trimming of excess geomembrane to obtain proper overlap
prior to seaming.
Figure 8.2. Type of scissors recommended for cutting of geomembranes.
87
-------
Figure 8.3(a). Formation of "fishmouth" with excessive slack in
upper geomembrane versus lower geomembrane.
Figure 8.3(b). Cutting of "fishmouth" along its centerline.
88
-------
Figure 8.3(c). Overlapping and seaming the ends of the upper
geomembrane to the lower geomembrane.
Figure 8.3(d). Patch over the entire area where "fishmouth" was located.
89
-------
(1) There generally should be some slack in the installed liner which
depends on the type of geomembrane, the ambient and anticipated
service temperatures, length of time the geomembrane will be
exposed, location of the facility, etc. This is a design
consideration and the Plans and Specifications must be project
specific on the amount and orientation of this slack.
(m) The sheets which are overlapped for seaming must be clean. If
dirty, they must be cleaned with dry rags and other appropriate
materials.
(n) The sheets which are overlapped for seaming must be free of moisture
in the seam area.
(o) Seaming is not allowed during rain or snow, unless proper
precautions are made to allow the seam to be made with dry
geomembrane sheets, e.g., within an enclosure or shelter.
(p) It is preferable not to have water-saturated soil beneath the
geomembrane during installation. Seaming boards help in this regard
by lifting the seams off the soil subgrade.
(q) If the soil beneath the geomembrane is frozen, the heat from hot air
seaming devices or any preheating lamps that may be used can thaw
the frost allowing water to be condensed onto the unbonded region
ahead of the seam being fabricated. This possibility may be
eliminated by the use of suitable seaming boards or slip sheets made
from excess geomembrane material.
(r) Ambient temperatures for seaming should be above freezing, i.e. 0°C
(32'F), unless it can be proven with test strips that good seams can
be fabricated at lower temperatures. However, temperature is less
of a concern to good seam quality than is moisture.
(s) For cold weather seaming, it may be advisable to preheat the sheets
with a radiant heater or hot air blower, to use a tent of some sort
to prevent heat losses during seaming and to make numerous test
seams in order to determine appropriate seaming conditions, e.g.,
equipment temperatures may have to be set higher and/or seaming
rates slowed down during cold weather seaming.
(t) Sheet temperatures for seaming should be below 50°C(122°F) as
measured by an infrared thermometer or surface contact thermocouple.
It is recognized that depending on material, type and thickness,
higher temperatures may be allowed. It should also be recognized
that wind and cloud cover will determine the actual sheet
temperature. High temperatures affect not only worker performance
but will also affect durability of some geomembranes unless special
precautions, e.g. tents, etc., are taken. For temperatures above
this value special attention should be paid to the seaming, frequent
test strips and more diligent nondestructive testing is recommended.
NOTE: For items (q), (r), (s,) and (t) the CQC/CQA Documents and/or
90
-------
project specifications and the regulatory requirements regarding hot
and cold temperature seaming limitations should be reviewed to avoid
possible problems with final construction certification acceptance.
8.2 EQUIPMENT PREPARATION
(a) Properly functioning portable electric generators must be available
within close proximity of the seaming region and with adequate
extension cords to complete the entire seam. These generators
should be of sufficient size or numbers to handle all seaming
electrical requirements. The generator must have rubber tires, or
be placed on a smooth plate such that it is completely stable so
that it cannot damage the geomembrane or to the underlying clay
liner or subgrade material. Fuel (gasoline or diesel) for the
generator must be stored off the geomembrane and if accidently
spilled on the geomembrane it must be immediately removed. The area
should be inspected for damage to the geomembrane and repaired if
necessary.
(b) Hot air seaming devices are of two different types: the manual,
hand-held type and the automatic, machine-driven type. Photographs
of each type are shown in Figure 8.4.
(c) If a gas, other than air, is to be used, an ample supply should be
available.
(d) A manual, hand-held instrument should be checked to see that the air
intakes are not obstructed and that the nozzle is of the proper type
and width and that it is free from obstructions which could limit a
uniform flow of air. Care should be taken in choosing the nozzle
design and magnitude of the pressure. If excessive air is
discharged under the top geomembrane it could create a backpressure
that may blow dust or small soil particles into the seam area. The
temperature should be capable of being monitored either with an
instrument gage or adjustment on the device or with a separate
temperature indicator. Typical temperature ranges for seaming
various geomembranes are given in Table 8.1.
(e) For the automatic, machine-driven type of hot air seaming equipment
there are a number of important details. As before, the air-flow
nozzle and temperature should be inspected to see that a constant
flow of air at the proper temperature is being supplied. Figure 8.5
gives general details of the system showing the relative positions
of the various parts.
(f) The air-flow nozzle should be checked to see if a single track or a
dual track seam is to be fabricated. If the latter, the nozzle will
be subdivided at its exit end into separated air flow channels.
91
-------
Figure 8.4. Various types of hot air seaming devices.
Upper photograph is a manual hand-held type;
Lower photograph is an automatic machine-driven type.
92
-------
TABLE 8.1. TYPICAL TEMPERATURE RANGES FOR HOT AIR SEAMING OF
GEOMEMBRANES (I.E., AS THE AIR EXITS THE CHAMBER).
Geomembrane
Type
CPE
CPE-R
CSPE-R
EIA
EIA-R
HOPE"*
PVC
PVC-R
VLDPE*"
Minimum*
•C CF)
245 (475)
245 (475)
245 (475)
370 (700)
370 (700)
400 (750)
370 (700)
370 (700)
350 (660)
Maximum**
*C CF)
650 (1200)
650 (1200)
650 (1200)
650 (1200)
650 (1200)
650 (1200)
650 (1200)
650 (1200)
650 (1200)
* For dry, warm weather seaming conditions
** For damp, cold weather seaming conditions
*** For textured or roughened HOPE or VLDPE sheet increase temperatures
about 40°C (72"F). Also, slower seaming rates and higher pressures
may be required.
93
-------
Lower FML
Nozzle
Seamed FML
Direction of Travel
Figure 8.5. Cross section of automated machine-driven hot air
seaming device for geomembranes.
I
(g) Knurled rollers are used for applying pressure on the sheets and
driving the device. They immediately follow the air nozzle. The
knurled rollers should be inspected to ensure there are no sharp
surfaces and that wheels are smoothly beveled on the edges.
(h) If a chain drive powers the device and applies pressure to the
nip/drive rollers it should be inspected for synchronization of
travel, proper functioning and fit. Loose chains or damaged
sprockets should be repaired or replaced.
(i) As the geomembrane sheet materials pass through the machine, they
should come in contact with air from the full width of the air
nozzle in order to heat the material properly and uniformly. On
some devices idler rollers on both sides of the device are
adjustable and must make the material conform as it passes through
the machine.
(j) The front part of the seaming device should be inspected for sharp
corners and irregular details which may damage the geomembrane or
cause sheet hang-up.
94
-------
(k) If available, temperature controllers on the device should be set
according to type of geomembrane, the thickness, the ambient
temperature, and the rate of seaming. Table 8.1 gives typical
values but this is a site and material specific decision usually
determined by the contract specification or CQC/CQA Documentation.
(1) If available, the force sensors at the nip rollers should be
checked for accuracy and repeatability.
8.3 TEST STRIPS
A general requirement of most CQA Documents is that "test seams" or
"test strips" be made on a periodic basis. Test strips generally reflect the
quality of field seams but should never be used solely for final field seam
acceptance. Final field seam acceptance should be specified in the contract
specification and should include a minimum level of destructive testing of
the production field seams. Test strips are made to minimize the amount of
destructive sampling/testing which requires subsequent repair of the final
field seam. Typically these test seams, for each seaming crew, are made
about every four hours, or every time equipment is changed, or if significant
changes in geomembrane temperature are observed, or as required in the
contract specification. This is a recommended practice that should be
followed when seaming all types of geomembranes. The purpose of these tests
is to establish that proper seaming materials, temperatures, pressures,
rates, and techniques along with the necessary geomembrane pre-seaming
preparation is being accomplished. Test strips may be used for CQA/CQC
evaluation, archiving, for exposure tests, etc., and must be of sufficient
length to satisfy these various needs.
Each seaming crew and the materials they are using must be traceable and
identifiable to their test seams. While the test seams are being prepared,
cured, and CQC tested, the seaming crew may continue to work as long as the
seams they have made (and are making) since their last acceptable test sample
strip was prepared, are completely traceable and identifiable. If a test
seam fails to meet the field seam design specification, then an additional
test seam sample will have to be made by the same seaming crew - using the
same tools, equipment and seaming materials - and retested.
The liner's finished field seams will not be accepted unless the before
and after "test seam sample strip" CQC test results (or other CQC seam test
result criteria as required per the design specification) are acceptable per
the site's design specifications. If a seam is not accepted, destructive
testing of samples from the actual seam will be removed from the liner and
tested. If the actual seam destructive test results still do not meet the
design specification requirement, then the unacceptable seams will all have
to be repaired or reconstructed with seaming materials by a test proven
seaming crew that has passed its testing requirements. The procedure
illustrated in the flow chart of Figure 8.6 must be followed. Note that the
failure of test strip 1 requires two actions: (a) the making of test strip
2, and (b) an increased frequency of destructive tests on production field
seams made during the curing of test strip 1 (if any were made). This
95
-------
I
'Mot*: S*tm/ng CnwFilling to Pnptn
AccipttUt TtaStrtptUiyfttguIn
attaining InAeeonltnet with COC/COA Ooamtntt
Figure 8.6. Test strip process flow chart.
96
-------
increased frequency must be stipulated in the contract specifications or in
the CQC/CQA Documents.
If the destructive seams fail or if test strip 2 fails, production field
seaming is halted. All production field seams made during the interval are
repaired per the contract specifications or CQC/CQA Documents to the point of
previous acceptance with an approved seaming crew.
At this point, the seaming crew that failed to pass both strip tests
must adjust and recertify current seaming equipment and technique or obtain
new seaming equipment, tools and/or retrain personnel and begin making
initial test strip samples.
For hot air seams, test strips of the type shown in Figure 8.7(a-d) are
prepared. The seam is centered lengthwise between the two sheets to be
joined. Figure 8.7(a) shows the geomembrane to be seamed being cut and
prepared for seaming, 8.7(b) shows the actual test strip being seamed, 8.7(c)
shows the sampling of the test strip for subsequent destructive testing, and
8.7(d) shows the individual samples cut from the test strip being identified.
For geomembranes that are seamed by thermal methods, the seams can be tested
after they are allowed to cool in ambient air at least 5-10 minutes or longer
prior to shear and peel testing.
As previously stated, all seam test samples must be prepared in
triplicate sets preferable in a continuous seam which can be cut in thirds;
one set for CQC tests, one set for CQA tests and one set made available to
(or retained for) the agency/owner/design organization. If referee test
results are required, CQA test results from destructive testing of actual
seam samples will prevail.
During the CQC and CQA test requirement periods, a liner should not be
covered and it cannot be placed into service. This will insure the ease and
viability of repairing or reconstructing in the event it is required. During
this period it is imperative that the liner be properly ballasted and
otherwise secured so as to prevent wind or unusual weather damage.
8.4 ACTUAL SEAMING PROCESS FOR THE MANUAL, HAND-HELD TYPE OF HOT AIR SEAMING
(a) The hot air system should be properly positioned for the making of
the desired seam, see Figure 8.8. Note the position of the
hand-held roller immediately behind the gun.
(b) The principle of the technique is that the hot air is to melt the
surface of both the lower and the upper geomembrane followed
immediately by roller pressure to intimately join the melted
viscous surfaces of the materials. Uniformity of melting across
the entire surface to be joined is an important detail. Excessive
97
-------
Figure 8.7(a). Geomembrane being cut and prepared for trial seaming.
Figure 8.7(b). The two sheets being seamed together thereby
forming the test strip.
98
-------
Figure 8.7(c). The completed test strip being cut into individual samples
for subsequent inspection and destructive testing.
Figure 8.7(d). Marking the test strip samples for identification
and records.
99
-------
4
Figure 8.8. Fabrication of a field seam using manual hand-held
hot air seaming technique.
melting as well as inadequate melting must be avoided. Note that
the roller pressure is exerted manually.
(c) Temperature and dwell time will vary according to the geomembrane
type, thickness and the ambient temperature. These variables, in
turn, will dictate the rate of seaming.
(d) Other ambient factors such as sun, clouds, wind and humidity will
require alterations to the seaming rate. This is a site specific
consideration.
(e) It is necessary that the seamer(s) keep constant visual contact
with the completed seam.
(f) It is sometimes advantageous to have two man work crews; one with
the hot air gun, the other with the roller. The second person is
then somewhat free to do visual and hands on inspection.
(g) Excessive surface deformation indicating too much heat, or too
slow of a travel rate, are obviously not permitted.
100
-------
8.5 ACTUAL SEAMING PROCESS FOR THE AUTOMATED, MACHINE-DRIVEN TYPE OF HOT AIR
SEAMING
(a) The hot air equipment should be properly positioned for the making
of the desired single or dual (split) seam, see Figure 8.9(a-b).
(b) As mentioned previously, the principle of the hot air seaming
technique is that both surfaces to be joined come into intimate
contact with one another after reaching the proper temperature.
Contact is automatically controlled via the rollers which create
pressure such that intermingling of the material from both sheets
occurs.
(c) Typical temperature settings will vary according to the type and
thickness of geomembrane being installed, the ambient temperature
and the rate of travel. The CQC/CQA Documentation should be
reviewed for appropriate temperature ranges.
(d) Ambient factors such as sun, clouds, wind, and humidity will
require the seaming rate to vary. This is a site specific
condition.
(e) Power for the drive motor should be off when positioning the
machine to make a seam. Manually place the machine within the
overlapped sheets of material. The sheets shall be guided beneath
and above the air nozzle, and into the drive/nip rollers. This
procedure is only possible when starting with two new sheets.
When restarting a partially completed run in the middle of two
sheets, the material must be loaded from the sides. The machine
is to be picked up a few inches, loading the bottom sheet first,
and then the top sheet. As soon as the nip rollers are engaged,
the hot air should be supplied to the sheets and the power to the
drive motor should be turned on.
(f) It is necessary that the operator keep constant visual contact
with the completed seam coming out of the machine. Occasional
adjustments of temperature or speed will be necessary to maintain
a consistent seam weld.
(g) On some soils, the machine may "bulldoze" into the ground as it
travels. This causes soil to enter the area to be seamed, making
the seam weak and unacceptable. To overcome this, it is
recommended that the operator take some of the weight off the back
of the machine by lifting it slightly. Alternatively, some type
of base for the machine to travel on could be provided. Strips of
geotextile or geomembrane have proven effective to prevent this
bulldozing effect. It might be required to change the size of the
rollers. It is recommended that at least two people work together
in making hot air seams; one operator and one helper.
101
-------
Figure 8.9(a). Fabrication of a field seam using automated, machine
driven hot air seaming technique (side view).
I
Figure 8.9(b). Fabrication of a field seam using automated, machine
driven hot air seaming technique (top view).
102
-------
(h) A leak-proof T-connection is necessary wherever intersecting seams
are to be joined together. At such locations when HOPE or VLDPE
geomembrane is used, the hot air device must be removed a short
distance (approximately 15 cm or 6 inches) from the intersecting
seam. This short distance must be completed by hand held hot air
seaming, or by extrusion fillet seaming, see Figure 8.10. Note
that the unbonded free overlaps of the sheets are to be cut away
to expose the edge of the outside of the hot air seam. The
extrudate bead is then placed in a continuous fashion so as to
provide complete coverage of all areas not completed by the hot
air device.
(i) For leak proof T-connections in PVC, CSPE, CPE and EIA materials,
the short distance referred to in (h) above must be completed by
chemical bonding (fusion) or chemical adhesive.
8.6 AFTER SEAMING
(a) A smooth insulating plate or heat insulating fabric is to be
placed beneath the hot seaming apparatus after usage to avoid
damage to the geomembrane.
(b) A slight amount of "squeeze-out" or "flashing" is a good indicator
that the proper temperatures were achieved, see the sketches of
Figure 8.11. It signifies a proper seam in that some of the
melted polymer was laterally squeezed out of the seam zone. If an
excessive amount of hot melt is being squeezed out, it is an
indication of either too much heat, too much pressure, or too slow
a seaming rate. Reduce the temperature and/or pressure and/or
adjust the rate to correct the situation.
(c) For VLDPE liners of 1.0 mm (40 mils) thickness, a long, low
wavelength pattern in the direction of the seam along its top
surface is indicative of a proper weld. If the wave peaks become
too close together, the machine speed should be increased until a
satisfactory pattern is present. The absence of this wavelength
pattern indicates that the speed should be decreased. There will
be no wavy pattern for VLDPE liners greater than 1.0 mm (40 mils)
in thickness due to the inherent stiffness of the thicker
material.
(d) Nip/drive roller marks may show on the surface when using knurled
rollers. Their depth should be visually observable, but care
should be taken to insure that the nip drive rollers do not create
a rut, e.g. the indentation should be barely capable of being
felt.
(e) The hot air seaming device has only a few adjustments that can be
made, but it is very important that they be checked regularly.
Cleaning of machine should be done at least daily.
103
-------
Extrudate
Extrudate
/Hot air fusion
weld
SECTION
fillet extrusion bead
Figure 8.10. Dual track hot air machine T-seam detail for HOPE or VLDPE.
104
-------
Upper Geomembrane
"Squeeze-Out" or
"Flashing*
typ. 25-75 mm
(1-3 in.)
Lower Geomembrane
Upper Geomembrane
"Squeeze-Out" or
"Flashir
typ. 12 mm
(0.5 in.)
typ. 12 mm
(0.5 in.)
typ. 12 mm
(0.5 in.)
Lower Geomembrane
Figure 8.11. Schematic diagrams of cross sections of single and
dual (spilt) hot air seams illustrating squeeze-out.
(f) The seam must be checked visually for uniformity of width and
surface continuity. Usually the installer will use a vacuum box
or air lance to check for voids or gaps in the seam.
(g) When unbonded areas are located, they should be patched with at
least 15 cm (6 inches) of geomembrane extending on all sides. Any
area of the geomembrane where puncture holes are observed must be
patched as above with at least 15 cm (6 inches) of geomembrane
extending beyond the affected areas.
(h) Photographs of cross sections of hot air seams follow in
Figure 8.12.
8.7 UNUSUAL CONDITIONS
This section is written to give insight into conditions which go beyond
the general description just presented.
(a) High winds, or gusts of wind, are always problematic for liners.
After placing the geomembrane, the panels or rolls must be
adequately ballasted, e.g., with sandbags. The actual seam
fabrication, however, may require the removal of some of the
sandbags leaving the windward edge vulnerable to wind uplift
forces.
105
-------
Figure 8.12. Cross sections of EIA-R liner (single track) seams fabricated
by the hot air method showing left, center, and right sides of
completed seam (light colored lines are the reinforcing fabric
yarns).
106
-------
If possible, proper orientation of the overlap might be helpful.
Otherwise, additional labor may be required to remove sandbags
immediately in front of the seaming operation. The liner must be
cleaned of any dirt and moisture left behind after sandbag
removal. They are then to be replaced behind the completed
seaming operation.
(b) Patches are necessary at locations where destructive test samples
are removed or where seams are shown to fail nondestructive
testing. These patches must extend a minimum of 15 cm (6 inches)
beyond the outer limits of the area to be repaired. For HOPE and
VLDPE liners, another method available is the hand-held extrusion
fillet procedure described in Section 5. Particular care must be
exercised when the end of the run meets the beginning of the run.
The double heat that the polymer will necessarily experience
cannot be excessive. For other geomembrane types, one or more of
the following methods may be used; hot air, chemical or adhesive
methods be used. These will be described in subsequent sections.
(c) Details around sumps, pipes and other appurtenances are perhaps
the most demanding locations to properly seam in an entire
facility. Also due to their typical locations being at low points
of the containment facility's design, these areas inherently
operate under larger hydraulic heads. Should a defect from
improper seaming occur in such a location leakage rates and its
associated adverse impacts are heightened. Therefore, extreme
care should be exercised in ensuring seam integrity in these often
difficult to reach locations. For HOPE and VLDPE liners these
details must necessarily be made by hand held hot air or extrusion
fillet procedures. For PVC, CSPE, CPE and EIA either hot air or
chemical fusion procedures can be used.
(d) This section was written for material temperatures that range
between 0°C (32'F) and 50°C (122*F). This is the temperature
range that is general recognized as being acceptable for seaming
without taking special precautions.
For sheets below 0°C (32°F), shielding, pre-heating, and/or a
slower seaming rate may be required. More frequent seam testing
and precautions to prevent thawing subgrade (previously discussed)
may have to be taken. Sharp, frozen subgrade should be avoided to
eliminate point pressure damage potential.
For sheet temperatures above 50*C (122°F), shielding and rate of
seaming should be adjusted. More frequent destructive seam
testing may have to be taken.
107
-------
FIELD NOTES:
108
-------
SECTION 9
DETAILS OF CHEMICAL AND BODIED CHEMICALLY-FUSED SEAMS
As is shown in Table 4.2, chemically-fused seams are an applicable field
seaming method for PVC, CPE, CSPE, and EIA liners, both reinforced and
unreinforced. Fusion chemicals may be either bodied (thickened) or nonbodied.
The application and seaming procedure for the use of either one is basically
the same. Bodied fusion chemicals are thickened with materials that are also
common to the geomembrane itself. They may be used interchangeably with non-
bodied fusion chemicals; however, they are more commonly used to increase the
dwell or working time, seal exposed fabric or scrim edges or on slopes to
prevent rapid run-off of the seaming chemical. This section focuses on the use
of both forms of fusion chemicals as through they were a single entity for
field seaming compounded thermoplastic and thermoplastic elastomeric
geotnembranes.
9.1 GEOMEMBRANE PREPARATION
(a) Note that this document assumes that the geomembrane has been
visually inspected to ensure it is free of deep scratches or defects
that would cause the sheet to not meet the specifications of the
installation. It is further assumed the sheet has been delivered
to the site and brought to its approximate plan position (as per the
design panel layout) for final installation and seaming. Only the
material that can be seamed that day should be deployed. All
deployed material should be ballasted as required to prevent wind
uplift.
(b) The geomembrane will usually arrive on site in the form of
prefabricated panels which are accordion folded in both directions.
These panels are usually packaged in palletized, heavy weatherable
cardboard containers.
(c) The geomembrane should remain packaged and dry until ready for use.
The material should not be unfolded when material temperatures are
lower than -10'C (14°F) due to the possibility of cracking. If the
panel is stored in a warm place, e.g. 10°C (50°F) or above, prior to
being unfolded on site, then it can be placed at -18°C (0°F) or
below temperatures, providing the time between removing the
geomembrane from storage and deployment does not exceed one-half
working day. Geomembrane deployment may be allowed for other
conditions but the CQC/CQA Documents and/or project specifications
must be specific as to the conditions.
109
-------
(d) All personnel walking on the geomembrane liner should have smooth-
soled shoes. Heavy equipment, e.g. pickups, tractors, etc., should
not be allowed on the geomembrane unless otherwise specified by the
manufacturer and approved in the CQA/CQC Documents.
(e) The two geomembrane sheets to be joined must be properly positioned
so that approximately 15 cm (6 inches) of overlap exists. If the
overlap is insufficient, lift the geomembrane sheet up and down to
allow air to be pumped beneath it and "float" it into proper
position.
(f) If the overlap is excessive, the excess material may be trimmed with
scissors or worked away from the edges of the seam to maintain
proper overlap, as shown in Figure 9.1(a-b). All cut scrim edges
must be sealed with a flood coat of bodied chemical or the
manufacturer's/fabricator's approved liquid sealant.
(g) When reinforced geomembranes are cut to accommodate odd shapes or to
fit small pieces, resealing of the exposed scrim by flood coating is
required by the use of manufacturer's or fabricator's approved
liquid sealant. This sealant is usually a thickened chemical of the
same type used to do the production field seaming.
(h) All cutting and preparation of odd shaped sections or small fitted
pieces can be accomplished at the discretion of the installer so
that production field seaming can be completed with as few
interruptions as possible.
(i) The two opposing geomembrane sheets to be joined should be visually
checked for defects of sufficient magnitude to effect seam quality.
The criteria to be met and the procedures to be used in this regard
should be stipulated in the contract specifications and/or in the
CQC/CQA Documents.
(j) If the construction plans require overlaps to be shingled in a
particular direction, this should be checked.
(k) Excessive undulations (waves) along the seams during the seaming
operation should be avoided. When this occurs due to either the
upper or lower sheet having more slack than the other or because of
thermal expansion and contraction, it often leads to the undesirable
formation of "fishmouths" which must be trimmed, laid flat and
reseamed with a patch. An example of a fishmouth and its correction
is shown in Figure 9.2(a-c).
(1) There should be some slack in the installed liner which depends on
the type of geomembrane, the ambient and anticipated service
temperatures, length of time the geomembrane will be exposed,
location of the facility, etc. This is a design consideration and
the plans and specifications must be project specific on the amount
and orientation of this slack.
110
-------
Figure
Commended for
111
cutting of geomembranes.
-------
Figure 9.2(a). Formation of "fishmouth" resulting from excessive slack
in upper geomembrane versus lower geomembrane.
Figure 9.2(b). Cutting of "fishmouth" along its centerline.
112
-------
Figure 9.2(c). Patch over the entire area where "Fishmouth" was located.
(m) The sheets which are overlapped for seaming must be clean. If
dirty, they must be cleaned with dry rags. If processing aids were
used in the manufacture of the sheet, this must be removed.
(n) The sheets which are overlapped for seaming must be free of moisture
in the seam area.
(o) Seaming is not allowed during rain or snow, unless proper
precautions are made to allow the seam to be made with dry
geomembrane sheets, e.g., within an enclosure or shelter.
(p) It is preferable not to have water saturated soil beneath the
geomembrane during installation. Seaming boards help in this regard
by lifting the seams off the soil subgrade.
(q) If the soil beneath the geomembrane is frozen, the heat from hot air
guns or any preheating lamps that may be used can thaw the frost
allowing water to be condensed onto the unbonded region ahead of the
seam being fabricated. This possibility may be eliminated by the
use of suitable seaming boards or slip sheets made from excess
geomembrane.
(r) Sheet temperatures for seaming should be above freezing, i.e. O'C
(32°F) unless it can be proven with test strips that good seams
can be fabricated at lower temperatures. However, temperature is of
less concern to good seam quality than is moisture.
113
-------
I
(s) For cold weather seaming, it may be advisable to preheat the sheets
with a radiant heater, or hot air blower, or to use a tent of some
sort to prevent heat losses during seaming and to make numerous test
seams in order to determine appropriate seaming conditions.
(t) Sheet temperatures for seaming should be below 50°C (122°F) as
measured by an infrared thermometer or a surface contact
thermocouple. It is recognized that depending on material type and
thickness, higher temperatures may be allowed. It should also be
recognized that wind and cloud cover will determine the actual sheet
temperature. High temperatures affect not only worker performance,
but may also affect seam durability of some geomembranes unless
special precautions are taken. For temperatures above this value
special attention should be paid to the seaming, frequent test
strips and more diligent non destructive testing is recommended.
NOTE: For items (q), (r), (s,) and (t) the CQC/CQA Documents
and/or project specifications and the regulatory requirements
regarding hot and cold temperature seaming limitations should be
reviewed to avoid possible problems with final construction
certification acceptance.
9.2 EQUIPMENT PREPARATION
(a) An ample supply of the appropriate fusion chemicals must be
available at the job site. They should be stored at room
temperature and sheltered from the elements. Storage is to be away
from any portion of the geomembrane so that accidental spillage can
not occur on the liner itself, or over a diked retaining pad or
impoundment, so that chemicals cannot penetrate the ground. The
listed shelf life of the fusion chemical shall not be exceeded.
Fusion chemicals that have been left open and started to solidify
should not be remixed or used.
(b) An ample supply of plastic applicator bottles (or other suitable
applicators) with special end applicators should be available. Note
that the filling of these applicator bottles is to take place away
from the geomembrane area. See Figure 9.3 for the typical type of
applicator bottles and their use in applying the fusion chemicals.
(c) A 5 cm to 10 cm (2 to 4 inches) wide paint brush may be used to
apply bodied chemical to the area to be seamed. The bristles should
be made from materials which do not react with the chemical being
applied.
(d) Clean, dry rags and or sponges will be needed to clean the sheet
areas to be seamed as well as to wipe away excess chemical from the
seamed area after the seam is completed. These rags should be
chemically resistant to the bonding liquid. Lint-free natural fiber
rags made of cotton or wool are generally recommended.
114
-------
Figure 9.3. Photograph of applicator bottles and method of application.
(e) Pressure applicators including rollers, either steel, rubber, nylon
or wood depending on site specific conditions, from 5 to 9 cm (2 to
3 1/2 inches) wide, will be needed for applying pressure to the
bonded area after the fusion chemical has been applied. Figure 9.4
illustrates the types of rollers in common use. Pressure applied
with a rag or wood paddle has been successfully used in place of a
roller to achieve a good seam.
(f) Seaming boards or slip sheets should be available. They need to be
rigid enough to provide adequate resistive force for seaming
pressures. The seaming boards must be smooth with rounded corners
and edges and have a hole drilled at one end for attaching a pull
rope. If needed, they may serve as temporary working platforms
placed beneath the seaming area to provide a smooth surface and a
base for physical resistance to the applied pressure of the rollers.
They also provide insulation to heat and help keep dirt and moisture
away from the seaming area.
(g) Hot air guns or other appropriate heating devices are necessary to
heat the geomembrane when performing cold-temperature field seaming.
(h) For cold-temperature seaming, properly functioning electric
generators to power the heating devices or heat guns, must be
available within close proximity of the seaming region and with
adequate extension cords to complete the entire seam. These
generators should be of sufficient size or numbers to handle all
seaming and preheating electrical requirements. The generator must
have rubber tires, or be placed on a smooth plate such that it is
115
-------
Figure 9.4. Photograph of types of rollers used to apply
pressure to chemically bonded seams.
completely stable in order that it will not damage the geomembrane.
Fuel (gasoline or diesel) for the generator must be stored away from
the geomembrane and if accidently spilled on the geomembrane must be
immediately removed. The area should be inspected for damage to the
geomembrane and repaired if necessary.
9.3 TEST STRIPS
A general requirement of most CQA Documents is that "test seams" or "test
strips" be made on a periodic basis. Test strips generally reflect the quality
of field seams but should never be used solely for final field seam acceptance.
Final field seam acceptance should be specified in the contract specification
and should include a minimum level of destructive testing of the production
field seams. Test strips are made to minimize the amount of destructive
sampling/testing which requires subsequent repair of the final field seam.
Typically these test seams, for each seaming crew, are made about every four
hours, or every time equipment is changed, or if significant changes in
geomembrane temperature are observed, or as required in the contract
specification. This is a recommended practice that should be followed when
seaming all types of geomembranes. The purpose of these tests is to establish
that proper seaming materials, temperatures, pressures, rates, and techniques
along with the necessary geomembrane pre-seaming preparation is being
accomplished. Test strips may be used for CQA/CQC evaluation, archiving, for
exposure tests, etc., and must be of sufficient length to satisfy these various
needs.
116
-------
Each seaming crew and the materials they are using must be traceable and
identifiable to their test seams. While the test seams are being prepared,
cured, and CQC tested, the seaming crew may continue to worx as long as the
seams they have made (and are making) since their last acceptable test sample
strip was prepared, are completely traceable and identifiable. If a test seam
fails to meet the field seam design specification, then an additional test seam
sample will have to be made by the same seaming crew - using the same tools,
equipment and seaming materials - and retested.
The liner's finished field seams will not be accepted unless the before
and after "test seam sample strip" CQC test results (or other CQC seam test
result criteria as required per the design specification) are acceptable per
the site's design specifications. If a seam is not accepted, destructive
testing of samples from the actual seam will be removed from the liner and
tested. If the actual seam destructive test results still do not meet the
design specification requirement, then the unacceptable seams will all have to
be repaired or reconstructed with seaming materials by a test proven seaming
crew that has passed its testing requirements. The procedure illustrated in
the flow chart of Figure 9.5 must be followed. Note that the failure of test
strip 1 requires two actions: (a) the making of test strip 2, and (b) an
increased frequency of destructive tests on production field seams made during
the curing of test strip 1 (if any were made). This increased frequency must
be stipulated in the contract specifications or in the CQC/CQA Documents.
If the destructive seams fail or if test strip 2 fails, production field
seaming is halted. All production field seams made during the interval are
repaired per the contract specifications or CQC/CQA Documents to the point of
previous acceptance with an approved seaming crew.
At this point, the seaming crew that failed to pass both strip tests must
adjust and recertify current seaming equipment and technique or obtain new
seaming equipment, tools and/or retrain personnel and begin making initial test
strip samples.
For chemical fusion seams or bodied chemical fusion seams, test strips of
the type shown in Figure 9.6(a-d) are prepared as required by the contract
specification or CQC/CQA Documents. The seam is centered lengthwise between
the two sheets to be joined. Figure 9.6(a) shows the two geomembrane pieces to
be seamed being cleaned and properly aligned, 9.6(b) shows the chemical being
applied to bonding area, 9.6(c) shows the completed seam being smoothed and
rolled, 9.6(d) shows samples being cut from completed test strips for
subsequent destructive testing.
For geomembranes that are seamed by chemical fusion methods, on site CQC
testing requires time that, without accelerated curing, can range from a few
hours to days. Accelerated curing of seam test samples using an oven on site,
or another suitable heat source, can be accomplished at temperature ranges
between 50°C (122"F) and 70°C (158°F) within periods that range from 1 hour to
16 hours, dependent upon the following variables: material type, thickness,
chemical fusion system, seam width, etc. After the accelerated curing period
the samples are allowed to cool at least 1/2 hour prior to CQC peel and shear
117
-------
'Not*: S**mlng CnwFilling to Pnptn
Accipttt/f nastriptlliyfiK/u/n
Rttnlning InAcconltncf with CQC/C04. Document*
Figure 9.5. Test strip process flow chart.
118
-------
Figure 9.6(a). Alignment of test strip and cleaning of area to
be bonded.
Figure 9.6(b). Applying fusion chemical to area of lower geomembrane
to be bonded.
119
-------
Figure 9.6(c). Smoothing and rolling bonded area.
I
Figure 9.6(d). Cutting the test strip samples for appropriate
groups for testing or storage.
120
-------
testing. Volatile chemical odors should no longer be detected. The exact
procedures should be specifically written into the CQC/CQA Documents.
During the CQC and CQA test requirement periods, a liner should not be
covered and it cannot be placed into service. This will insure the ease of
repairing or reconstructing in the event it is required. During this period it
is imperative that the liner be properly ballasted and otherwise secured so as
to prevent wind or unusual weather damage.
9.4 ACTUAL SEAMING PROCESS
(a) Position the geomembrane panels so that the entire length of the
seam area overlaps. If required for site specific considerations,
place the desired length of seaming board or slip sheet beneath the
seam and correctly position it so as to provide a good working
surface for the area to be seamed, see Figure 9.7.
(b) Use a fine bristle brush, clean rags, or other means to remove soil
particles or dust from the area to be seamed.
(c) If two seaming crews can work simultaneously on the same seam, begin
seaming at the mid-point of the geomembrane panels and work toward
the ends. This tends to prevent fishmouths occurring in the center
of the panel. On slopes, seaming should proceed uphill.
(d) In constructing field seams one invariably encounters areas where
three thicknesses of material need to be bonded together. These
areas occur at the intersection of factory and field seams and are
known as "T" connections, see Figure 9.8 for schematic
representation of the "T" connection. Either additional fusion
chemical should be used in these areas to bond the loose flap or the
loose portion of the flap should be trimmed off.
(e) A "T" trimming tool in action is pictured in Figure 9.9 showing the
trimming of the flap in the lower geomembrane. The "T" trimming
tool resembles a cheese cutter with a replaceable razor blade
cutting edge. It is only used to trim nonreinforced geomembranes
like PVC or unreinforced CSPE and CPE and then only for geomembranes
greater than 0.75 mm (30 mils).
For reinforced geomembranes one should discourage this type of
trimming because it exposes the scrim reinforcement. Such exposed
scrim should be avoided since moisture and/or leachate could wick up
the scrim and cause delamination or other undesirable effects.
Reinforced geomembranes should be trimmed as accurately as possible
with a razor hook knife, with a backing to prevent damage to the
underlying geomembrane. In all locations where the ends of scrim
are exposed one should use bodied adhesive chemicals or sealants
which, due to their higher viscosity, can be more generously applied
(called "flood coating") in these regions. All exposed scrim should
be sealed.
121
-------
Rope for I
advancing)*
seaming
board
fck^
j\
t
s
' ^ — Upper Geomembrane A
' Edge of Lower Geomembrane
'>x;
/
'£ ^
.50 mm (2 in.) Unbonded Overlap
k 100 mm (4 in.)
50 mm (2 in.) Seam Width Overlap Width
• X/ // // // // //y^
>v I
250 mm
Seaming
^/l
\ i
(10 in.)
Board
Edge of Upper Geomembrane
^~- Lower Geomembrane •
Direction of Seaming
bonded . ^— unbonded
.50 mm .50 mm
Upper Geomembrane
(2 in.)
Lower Geomembrane
Section A-A
Seaming Board
Figure 9.7. Positioning of wooden "seaming board" beneath seam
area of liner to provide for a uniform and smooth
subsurface.
122
-------
Factory Seams (previously made)
^^
Panel "A"
/
Field Seam
(to be made)
Field Seam "V-ower Edge
of Panel
Figure 9.8. Perspective diagram of locations where "T" configurations
commonly occur.
Figure 9.9. Photograph of "T" trimming tool shaving the upper
surface of an existing seam in preparation of new
intersecting seam.
123
-------
(f) The appropriate fusion chemical is applied with an applicator
(squeeze botle or brush) until it completely wets the bottom
geomembrane. Care must be taken to make sure that enough fusion
chemical is applied to wet and fuse both surfaces that are being
seamed. This adequate coverage can be seen since properly wetted
areas appear different than non-wetted areas. Any excess fusion
chemical should be wiped up quickly to prevent puddling, which could
damage the geomembrane, see Figure 9.10.
(g) After applying the fusion chemical, an "initial reaction" time, or
"dwell" time is required for the chemical to soften the surface of
the geomembrane sheet. Dwell times for various thicknesses of
different geomembranes are from 2 to 5 seconds. Note that high
ambient temperatures, strong wind, and low relative humidity all
tend to reduce the time necessary for the fusion chemical to soften
the surface of the sheet. Therefore, if these conditions exist, the
"dwell time" will be decreased. The determination of dwell time
emphasizes the importance of the preparation and testing of test
strips which were described earlier.
(h) Following the dwell time, the two liner surfaces are mated together
and pressure is applied to the upper surface. The pressure is
applied with a roller or other suitable pressure device. The process
involves rolling the seam both in a parallel and a perpendicular or
45 degree direction so as to mate and fuse the two liner surfaces,
remove air pockets, and to force any excess fusion chemical toward
and out of the exposed overlap edge. The seaming technician should
make a sufficient number of passes with the roller to insure that
both surface mating and excess chemical removal has been
accomplished. Generally between 5-10 passes in each direction over
a 60 cm (2 ft.) length will be needed, see Figure 9.11(a-b).
However, the use of any alternative chemical or pressure applicators
must be evaluated with test strip seams.
(i) Rolling should be accomplished using uniform pressure in a flowing
motion. This will lead to an acceptable seam with no entrapped
vapor or air pockets. Excessive pressure, e.g. pressure that would
cause the material to indent or crease, is not required.
(j) After applying pressure to a section of seam, any excess fusion
chemical should be wiped off the top of the geomembrane. Wipe
toward the leading edge of the seam not away from it. For
reinforced geomembranes it is desirable to see a small bead of
fusion chemical extend to the outer edge of the seam.
(k) Clean pressure applicators should be used at all times. When a
roller is used, a clean surface must be maintained.
124
-------
Figure 9.10. Application of fusion chemical.
^ x
^
\
\
^
. Upper Geomembrane
> 50 nV72 in> N N N \ \ \
'UnbondedtiLZona ....„ ...
^ T c
Seam iZone ' t
(finish^
1 Approximately 60 cm
^ Lower Geomembrane
Edge of Lower
J Geomembrane
\ N \ X\NV
(start) 100 mm (4 in.)
*~ } Overlap Zone
^ 5 passes
/ s I/ / /\t/
, 1^
(2 ft)l \EdgeofUpper
Geomembrane
Figure 9.11(a). Parallel rolling motion for the fabrication
of chemically fused seams.
125
-------
/SO mm (2 in.)
Seam I Zone
pproximately 60 cm (2 ft.]
8 passes
Lower Geomembrane
Edge of Lower
Geomembrane
100 mm (4 in.)
Overlap Zone
Edge of Upper
Geomembrane
Figure 9.11(b).
Perpendicular rolling motion for the fabrication
of chemically fused seams.
9.5 AFTER SEAMING
(a) The seam must be checked visually for uniformity of width and
surface continuity. As stated earlier, proper fusion chemical
application visually changes the surface appearance. Usually the
installer will use an air lance or blunt-end pick, see Figure
9.12(a-b), to check for voids or gaps under the overlapping
geomembrane.
(b) When unbonded areas are located, they can sometimes be repaired
by inserting more bonding agent into the opening and applying
pressure. If that is not satisfactory, a patch must be placed
over them with at least 15 cm (6 inches) of geomembrane extending
on all sides.
(c) Any area of the geomembrane sheets where fusion chemical
accidentally spilled and caused damage greater than 10% of the
original thickness, must be patched as above, with at least 15
cm(6 inches) of geomembrane extending beyond the affected areas.
(d) Any area of the geomembrane sheets where puncture holes are
observed must be patched as above, with at least 15 cm (6 inches)
of geomembrane extending beyond the affected areas.
126
-------
(a) Air lance test.
(b) Pick test.
Figure 9
.12. Photographs of air lance and pick testing of completed sea..
127
-------
(e) Note that with the above three repair items (b, c, and d) it is
not practical to use a seaming board beneath the geomembrane.
However, a piece of the liner material can be used for added
support under the liner, if needed, even if the hole must be
enlarged to insert the piece before the patch is made. This
added piece is left there indefinitely. In either situation,
additional care should be used to insure a proper bond.
(f) At the completion of seaming, all rags, chemical containers,
etc., should be properly removed from the geomembrane.
(g) Sand bags used to resist wind uplift stresses may be placed on
the seamed areas in accordance with customary installation
practice, as prescribed in the contract specifications, or
CQC/CQA Documents.
(h) Cross sections of the completed seams are shown in Figure
9.13(a-c).
9.6 UNUSUAL CONDITIONS
This section is written to give insight into conditions which go
beyond the general description just presented.
(a) High winds, or gusts of wind, are always problematic for liners.
After deploying the geomembrane, the panels should be adequately
ballasted, e.g., with sandbags. The actual seaming operation,
however, may require the removal of some of the ballast leaving
the windward edge vulnerable to wind uplift forces. If
possible, proper orientation of the overlap might be helpful.
Otherwise, additional labor may be required to only remove
sandbags immediately in front of the seaming operation. The
liner must be cleaned of any dirt and moisture left behind after
sandbag removal. They are then to be replaced behind the
completed seaming operation.
(b) Patches are invariably necessary to make at locations where
destructive test samples are removed or where seams are shown to
fail nondestructive testing. These patches must extend a
minimum of 15 cm (6 inches) beyond the outer limits of the area
to be repaired. Since a seaming board cannot be used in these
areas, additional care is necessary. Sometimes excess pieces of
geomembrane material, which are left in place, are positioned
beneath the area to be seamed.
128
-------
Figure 9.13(a). Cross sections of PVC liner seams prepared by
the chemical fusion method showing left side of
completed seam.
Figure 9.13(b).
Cross sections of PVC liner seams prepared by the
chemical fusion method showing center of completed
seam.
129
-------
Figure 9.13(c).
Cross sections of PVC liner seams prepared
by the chemical fusion method showing right
side of completed seam.
(c) Details around sumps, pipes and other appurtenances are perhaps
the most demanding locations to properly seam in an entire
facility. Also due to their typical locations being at low
points of the containment facility's design, these areas
inherently operate under larger hydraulic heads. Should a
defect from improper seaming occur in such a location leakage
rates and its associated adverse impacts are heightened.
Therefore, extreme care should be exercised in ensuring seam
integrity in these often difficult to reach locations. The
fusion chemical should be placed symmetrically on both liners to
be joined which may be difficult for external and internal edges
and particularly at corners. Hand and finger pressure may be
needed in tight areas.
(d) This section was written for material temperatures that range
between 0"C (32'F) and 50°C (122°F). This is the temperature
range that is generally recognized as being acceptable for
seaming without taking special precautions.
For sheet temperatures below 0°C (32°F), shielding, pre-heating,
different chemical compounds and/or a slower seaming rate may be
required. More frequent seam testing and precautions to prevent
thawing subgrade (previously discussed) may have to be taken.
Sharp, frozen subgrade should be avoided to eliminate point
pressure damage potential.
For sheet temperatures above 50°C (122°F) shielding and rate of
seaming should be adjusted. More frequent destructive seam
testing may have to be taken.
130
-------
FIELD NOTES:
131
-------
FIELD NOTES:
132
-------
SECTION 10
DETAILS OF CHEMICAL ADHESIVE SEAMS
As is shown in Table 4.2, chemical adhesive seaming represents an
applicable field seaming method for PVC, CPE, EIA, CSPE liners, both
reinforced and unreinforced. Adhesives differ from other bonding agents in
that they necessarily contain materials that are dissimilar to the liner
material itself. In addition to seaming adhesives, they are also sometimes
used to seal exposed fabric or scrim. This section focuses only on the use of
adhesives for seaming compounded thermoplastic and thermoplastic elastomeric
geomembranes.
10.1 GEOMEMBRANE PREPARATION
(a) Note that this document assumes that the proper geomembrane has
been visually inspected to ensure it is free of deep scratches or
defects that would cause the sheet to not meet the specifications
of the installation. It is further assumed the sheet has been
delivered to the site and brought to its approximate plan position
(as per design the panel layout) for final installation and
seaming. Only the material that can be seamed that day should be
deployed. All deployed material should be ballasted immediately to
prevent wind uplift.
(b) The geomembrane will usually arrive on site in the form of
prefabricated panels which are accordion-folded in both directions.
These panels are usually packaged in palletized, heavy weatherable
cardboard containers.
(c) The geomembrane should remain packaged and dry until ready for use.
The material should not be unfolded when material temperatures are
lower than -10"C (14°F) due to the possibility of cracking. If the
panel is stored in a warm place, e.g. 10°C (50'F) or above, prior
to being unfolded or unrolled on site, then it can be placed at
-18"C (0°F) or below temperatures providing the time between
removing the geomembrane from storage and deployment does not
exceed one-half working day. Geomembrane deployment may be allowed
for other conditions but the CQC/CQA Documents must be specific as
to the conditions.
(d) All personnel walking on the geomembrane should have smooth soled
shoes. Heavy equipment, e.g. pickups, tractors, etc., should not
be allowed on the geomembrane at any time, unless otherwise
specified by the manufacturer and approved in the CQC/CQA
Documents.
133
-------
(e) The two geomembrane sheets to be joined must be properly positioned
such that approximately 15 cm (6 inches) of overlap exists. If the
overlap is insufficient, lift the geomembrane sheet up and down to
allow air to be pumped beneath it and "float" it into proper
position.
(f) If the overlap is excessive, the excess material may be trimmed
with scissors or worked away from the edges of the seam to maintain
proper overlap, as shown in Figure 10.1 (a-b). All cut scrim edges
must be sealed with a flood coat of bodied adhesive or the
manufacturer's/fabricator's approved liquid sealant.
(g) When reinforced geomembranes are cut to accommodate odd shapes or
to fit small pieces, resealing of the exposed scrim by flood
coating is required by the use of manufacturer's or fabricators
approved liquid adhesive. This adhesive is usually a thickened
chemical of the same type used to do the production seaming as
described in Section 9.
(h) All cutting and preparation of odd shaped sections or small fitted
pieces can be accomplished at the discretion of the installer so
that production field seaming can be completed with as few
interruptions as possible.
(i) The two opposing geomembrane sheets to be joined should be visually
checked for defects of sufficient magnitude to affect seam quality.
The criteria to be met and the procedures to be used in this regard
should be stipulated in the contract specifications and/or in the
CQC/CQA Documents.
(j) If the construction plan requires overlaps to be shingled in a
particular direction, this should be checked.
(k) Excessive undulations (waves) along the seams during the seaming
operation should be avoided. When this occurs due to either the
upper or lower sheet having more slack than the other or because of
thermal expansion and contraction, it often leads to the
undesirable formation of "fishmouths" which must be trimmed, laid
flat and reseamed with a patch. An example of a fishmouth and its
correction is shown in Figure 10.2.(a-d).
(1) There should be some slack in the installed liner which depends on
the type of geomembrane, the ambient and anticipated service
temperatures, length of time the geomembrane will be exposed,
location of the facility, etc. This is a design consideration and
the plans and specifications must be project specific on the amount
and orientation of this slack.
(m) The sheets which are overlapped for seaming must be clean. If
dirty, they must be wiped clean with dry rags. If processing aids
were used in the manufacture of the sheet, this must be removed.
134
-------
Figure 10.1(a). Trimming of excess geomembrane sheet to obtain proper
overlap prior to seaming.
Figure 10.1(b). Type of scissors recommended for cutting of
geomembrane sheets.
135
-------
Figure 10.2(a). Formation of "fishmouth" resulting from excessive
slack in upper geomembrane versus lower geomembram
Figure 10.2(b). Cutting of "fishmouth" along its centerline
136
-------
Figure 10.2(c).
Overlapping and seaming the ends of the upper
geomembrane to the lower geomembrane.
Figure 10.2(d). Patch over the entire area where "fishmouth" was located.
137
-------
(n) The sheets which are overlapped for seaming must be completely free
of moisture in the seam area.
(o) Seaming is not allowed during rain or snow, unless proper
precautions are made to allow the seam to be made on dry
geomembrane sheets, e.g., within an enclosure or shelter.
(p) It is preferable not to have water-saturated soil beneath the
geomembrane during installation. Seaming boards help in this
regard by lifting the seams off the soil subgrade.
(q) If the soil beneath the geomembrane is frozen, the heat from hot
air guns and radiant lamps can thaw the frost allowing water to be
condensed onto the unbonded region ahead of the seam being
fabricated. This possibility may be eliminated by the use of
suitable seaming boards or slip sheets made from the excess
geomembrane.
(r) Ambient temperatures for seaming should be above freezing, i.e.
O'C (32°F), unless it can be proven with test strips that good
seams can be fabricated at lower temperatures. However,
temperature is of less concern to good seam quality than is
moisture.
(s) For cold weather seaming, it may be advisable to preheat the sheets
with a radiant heater, hot air blower, or to use a tent of some
sort to prevent heat losses during seaming and to make numerous
test seams in order to determine appropriate seaming conditions.
(t) Sheet temperatures for seaming should be below 50°C (122'F)as
measured by an infrared thermometer or surface contact
thermocouple. It is recognized that depending on material type and
thickness, higher temperatures may be allowed. It should also be
recognized that wind and cloud cover will determine the actual
sheet temperature. High temperatures affect not only worker
performance, but may also affect seam durability of some
geomembranes unless special precautions are taken. For
temperatures above this value special attention should be paid to
the seaming, frequent test strips and more diligent nondestructive
testing is recommended.
NOTE: For items (q), (r), (s,) and (t) the CQC/CQA Documents
and/or project specifications and the regulatory requirements
regarding hot and cold temperature seaming limitations should be
reviewed to avoid possible problems with final construction
certification acceptance.
10.2 EQUIPMENT PREPARATION
(a) An ample supply of the appropriate adhesive must be available at
the job site. It should be stored at room temperature and
sheltered from the elements. Chemical adhesives that have been
138
-------
left open and started to solidify should not be remixed or used.
Storage is to be away from any portion of the geomembrane so that
accidental spillage can not occur on the liner itself or over a
diked retaining pad or impoundment, so that chemicals cannot
penetrate the ground. The listed shelf life cannot be exceeded.
(b) A 5 cm to 10 cm (2 to 4 inches) wide paint brush will be needed to
apply adhesive to the area to be bonded. The bristles must be made
from materials which are not softened or dissolved by the adhesive.
(c) At least one clean paint can of a minimum capacity of 1/4 1 (1 pt.)
will be needed by each seaming crew. The can should only be filled
one third full to avoid spillage during the seaming process.
(d) A soft bristled brush and numerous rags will be needed to clean the
geomembrane to be seamed as well as wipe away any excess adhesive
after seaming. The brush and rags should be chemically resistant
to the adhesive.
(e) Pressure applicators including rollers, either steel, rubber, nylon
or wood depending on site specific conditions, from 5 to 9 cm (2 to
3-1/2 inches) wide, will be needed for applying pressure to the
bonded area after the adhesive has been applied. Figure 10.3
illustrates the types of rollers in common use. Pressure applied
with a rag or wood paddle has been successfully used in place of a
roller to achieve a good seam.
Figure 10.3. Photograph of types of rollers used to
apply pressure to solvent adhesive seams.
139
-------
(f) An ample supply of adhesive resistant gloves will be necessary to
eliminate the possibility of the adhesive coming in contact with
the skin.
(g) Seaming boards made from wooden planks or slip sheets should be
available. The seaming boards must be smooth with rounded corners
and edges and have a hole drilled at one end for attaching a pull
rope. If needed, they may serve as temporary working platforms
placed beneath the seaming area to provide a smooth surface and a
base for physical resistance to the applied pressure of the
rollers. They also provide insulation to heat and help keep dirt
and moisture away from the seaming area.
(h) Hot air guns or other appropriate heating devices are necessary to
heat the geomembrane when performing cold temperature field
seaming.
(i) For cold temperature seaming, properly functioning electric
generators to power the heating devices or heat guns, must be
available within close proximity of the seaming region and with
adequate extension cords to complete the entire seam. These
generators should be of sufficient size or numbers to handle all
seaming electrical requirements. The generator must have rubber
tires, or be placed on a smooth plate such that it is completely
stable in order that it will not damage the geomembrane. Fuel
(gasoline or diesel) for the generator must be stored away from
the geomembrane and if accidently spilled on the geomembrane must
be immediately removed. The area should be inspected for damage
to the geomembrane and repaired if necessary.
10.3 TEST STRIPS
A general requirement of most CQA Documents is that "test seams" or "test
strips" be made on a periodic basis. Test strips generally reflect the
quality of field seams but should never be used solely for final field seam
acceptance. Final field seam acceptance should be specified in the contract
specification and should include a minimum level of destructive testing of the
production field seams. Test strips are made to minimize the amount of
destructive sampling/testing which requires subsequent repair of the final
field seam. Typically these test seams, for each seaming crew, are made about
every four hours, or every time equipment is changed, or if significant
changes in geomembrane temperature are observed, or as required in the
contract specification. This is a recommended practice that should be
followed when seaming all types of geomembranes. The purpose of these tests
is to establish that proper seaming materials, temperatures, pressures, rates,
and techniques along with the necessary geomembrane pre-seaming preparation is
being accomplished. Test strips may be used for CQA/CQC evaluation,
archiving, for exposure tests, etc., and must be of sufficient length to
satisfy these various needs.
140
-------
Each seaming crew and the materials they are using must be traceable and
identifiable to their test seams. While the test seams are being prepared,
cured, and CQC tested, the seaming crew may continue to work as long as the
seams they have made (and are making) since their last acceptable test sample
strip was prepared, are completely traceable and identifiable. If a test seam
fails to meet the field seam design specification, then an additional test
seam sample will have to be made by the same seaming crew - using the same
tools, equipment and seaming materials - and retested.
The liner's finished field seams will not be accepted unless the before
and after "test seam sample strip" CQC test results (or other CQC seam test
result criteria as required per the design specification) are acceptable per
the site's design specifications. If a seam is not accepted, destructive
testing of samples from the actual seam will be removed from the liner and
tested. If the actual seam destructive test results still do not meet the
design specification requirement, then the unacceptable seams will all have to
be repaired or reconstructed with seaming materials by a test proven seaming
crew that has passed its testing requirements. The procedure illustrated in
the flow chart of Figure 10.4. must be followed. Note that the failure of
test strip 1 requires two actions: (a) the making of test strip 2, and (b) an
increased frequency of destructive tests on production field seams made during
the curing of test strip 1 (if any were made). This increased frequency must
be stipulated in the contract specifications or in the CQC/CQA Documents.
If the destructive seams fail or if test strip 2 fails, production field
seaming is halted. All production field seams made during the interval are
repaired per the contract specifications or CQC/CQA Documents to the point of
previous acceptance with an approved seaming crew.
At this point, the seaming crew that failed to pass both strip tests must
adjust and recertify current seaming equipment and technique or obtain new
seaming equipment, tools and/or retrain personnel and begin making initial
test strip samples.
For adhesive seams, test strips of the type shown in Figure 10.5(a-e) are
prepared. The seam is centered lengthwise between the two sheets to be
joined. Figure 10.5 (a) shows the two geomembrane pieces to be seamed being
cleaned and properly aligned, 10.5 (b) shows chemical adhesive being applied
to bonding area, 10.5 (c) shows adhesive in "tack" stage, 10.5 (d) shows
samples being cut from completed test strips for subsequent destructive
testing and 10.5 (e) shows the individual samples cut from the test strip
being identified.
For geomembranes that are seamed by adhesive methods, on site CQC testing
requires time that, without accelerated curing, can range from a few hours to
days. Accelerated curing of seam test samples using an oven on site, or
another suitable heat source, can be accomplished at temperature ranges
between 50'C (122*F) and 70°C (158'F) within periods that range from 1 hour to
16 hours, dependent upon the following variables: material type, thickness,
adhesive system, seam width, etc. After the accelerated curing period the
samples are allowed to cool at least 1/2 hour prior to peel and tensile/shear
141
-------
'Hoi*: Sttmlng CnwFMng to Pnptn
Accipttblt Tut Strip* MtyRtquIn
Kttnlnlng IttAccordtnct wHh CQC/CQA Doamntt
Figure 10.4. Test strip process flow chart.
142
-------
Figure 10.5(a). (Upper Left) Alignment of test strip and cleaning of area to
be area to be bonded.
Figure 10.5(b). (Lower Right) Applying chemical adhesive to area of lower
geomembrane to be bonded.
143
-------
Figure 10.5(c). Adhesive in the "tack" stage.
Figure 10.5 (d). Cutting samples from completed test strips.
144
-------
Figure 10.5(e).
Marking the test strip samples for appropriate
groups for testing or storage.
testing. Volatile chemical odor should no longer be detected. The exact
procedure should be specifically written into the CQC/CQA Documents.
During the CQC and CQA test requirement periods, a liner should not be
covered and it cannot be placed into service. This will insure the ease of
repairing and reconstructing in the event it is required. During this period
it is imperative that the liner be properly ballasted and otherwise secured so
as to prevent wind or unusual weather damage.
10.4 ACTUAL SEAMING PROCESS
(a) Position the geomembrane panels so that the entire length of the
seam area overlaps. If required for site specific considerations,
place the desired length of seaming board or slip sheet beneath the
seam and correctly position it so as to provide a good working
surface for the area to be seamed, see Figure 10.6.
(b) Use a fine bristle brush or rag to remove soil particles or dust
from the area to be seamed.
(c) If two seaming crews can work simultaneously on the same seam,
begin seaming at the mid-point of the geomembrane panels and work
toward the ends. This tends to prevent fishmouths occurring in
the center of the panel. On slopes, seaming should proceed
uphill.
145
-------
Rope for
advancing
seaming
board
v /£
\/
RlLx;
ik rj1""""'""1"
L V{ ^
k *
k \\
Upper Geomembrane
» of Lower Geomembrane
t> \ \ \ \ \ X "V \\\ \\ N
f50 mm (2 in.)
^Unbonded Overlap 1SO mm" (6 in-)
100 mm (4 in.) OverlaP Width
Seam Width
/// // // / / / / / / A
A^~1
,J
^ 1
250 mm
Seaming
-------
(d) In constructing field seams one invariably encounters areas where
three thicknesses of material need to be bonded together. These
areas occur at the intersection of factory and field seams and are
known as "T" connections, see Figure 10.7 for schematic
representation of the "T" connection. Either additional adhesive
should be used in these areas to bond the loose flap or the loose
portion of the flap should be trimmed off, see Figure 10.8.
For reinforced georaembranes one should discourage this type of
trimming because it exposes the scrim reinforcement. Such exposed
scrim should be avoided since moisture and/or leachate could wick up
the scrim and cause delamination or other undesirable effects.
Reinforced geomembranes should be trimmed as accurately as possible
with a razor hook knife, with a backing to prevent damage to the
underlying geomembrane. In all locations where the ends of scrim
are exposed one should use bodied adhesive chemicals or sealants
which, due to their higher viscosity, can be more generously applied
(called "flood coating") in these regions. All exposed scrim should
be sealed.
(e) Adhesive is applied uniformly to the bottom of the upper sheet and
to the top of the lower sheet. This is a critical part of the
adhesive seaming process. Care must be taken to make sure that
enough adhesive is applied to wet and fuse both surfaces that are
being seamed. This adequate coverage can be seen visually since
properly wetted seams look different from non-wetted areas. Excess
adhesive must be wiped up quickly and prevented from puddling, which
could damage the geomembrane.
(f) After applying the adhesive, a dwell time is required for the
adhesive to soften the surface of the geomembrane sheets. Dwell
times for various thicknesses of different geomembranes are from 2
to 5 seconds. Note that high ambient temperatures, strong wind, and
low relative humidity all tend.to reduce the time necessary for the
adhesive to soften the surface of the sheet. Therefore, if these
conditions exist, the "dwell time" will be decreased. The
determination of dwell time emphasizes the importance of the
preparation and testing of test strips which were described earlier.
(g) Following the dwell time, the two liner surfaces are mated together
and pressure is applied to the upper surface. The pressure is
applied with a roller or other suitable pressure device. The
process involves rolling the seam both in a parallel and
perpendicular or 45 degree direction so as to mate and fuse the two
surfaces, to remove air pockets, and to force any excess adhesive
toward and out of the exposed overlap edge, see Figure 10.9(a-b).
The seaming technician should make a sufficient number of passes
with the roller to insure that both surface mating and excess
adhesive removal have been accomplished. Generally between 5-10
passes in each direction over a 60 cm (2 ft.) length will be needed.
However, the use of any alternative adhesive or pressure applicator
147
-------
Factory Seams^ (previously made) •
/
Field Seam
(to be made)
Field Seam "V-Ower Edge
of Panel
Figure 10.7. Perspective diagram of locations where
"T" configurations commonly occur.
Figure 10.8. Photograph of "T" trimming tool shaving the upper
surface of an existing seam in preparation of new
intersecting seam.
148
-------
Upper Geomembrane •
Edge of Lower
Geomembrane
N
X
\
\
s.
N cn X £. X XXXXXXXNX NW
IJ 50 mm (2 in.)
lynraonoBni tana ^.^ m (start)
Y ILTzona'"0 ( * ^ 5 passes
V / sv/ / s / /^ / / / / /' ' s )/ / A
(finish) j 1^
I Approximately 60 cm (2 ft.) Q<
^- — Lower Geomembrane ^
100 mm (4 in.)
Overlap Zone
I/
ge of Upper
somembrane
Figure 10.9(a). Initial rolling motion parallel to seam for the
fabrication of adhesive seams for CPE, CSPE, EIA
or PVC liners.
must be evaluated on the test strip seams. The area that is
rolled or pressed must be continuous.
(h) Rolling should be accomplished at a somewhat tacky stage using
uniform pressure in a flowing motion, see Figure 10.9(b). This
will lead to an acceptable seam with no entrapped vapor or air
pockets. Excessive pressure is not required.
Upper Geomembrane •
^ \
f Edge of Lower
/ Geomembrane
^ SO mm (2 in.)
±lnhonrinriV7flna,.^f..rt.gTj^- _. -^. ^ -
\ * i, * ,
/50mm (2 in.) I .. 1 .
. SeamlZone t r T. '
///*//s^J/.)/ L> .^
Approximately 60 cm (2 f£
1 8 passes
^- — Lower Geomembrane «^
art)
100 mm (4 in.)
Overlap Zone
'/
\ Edge of Upper
Geomembrane
Figure 10.9(b). Final rolling motion perpendicular to seam for the
fabrication of adhesive seams for CPE, CSPE, EIA or
PVC liners.
149
-------
I
(i) After rolling a section of seam, any excess adhesive should be wiped
off the top of the geomembrane. Wipe toward the leading edge of the
seam not away from it. For reinforced geomembranes it is desirable
to see a small bead of adhesive at the outer edge of the seam.
(j) With this seaming method the adhesive remains in the bonded area and
becomes a component of the seam.
(k) Clean pressure applicators should be used at all times. When a
roller is used, a clean surface must be maintained.
10.5 AFTER SEAMING
(a) The seam must be checked visually for uniformity of width and surface
continuity. As stated earlier, proper adhesive application visually
changes the surface appearance. Usually the installer will use an
air lance or blunt-end pick, see Figure lO.lO(a-b), to check for
voids or gaps under the overlapping geomembrane.
(b) When unbonded areas are located, they can sometimes be repaired by
inserting more adhesive into the opening and rolling. If that is not
satisfactory, a patch must be placed over them with at least 15 cm
(6 inches) of geomembrane extending on all sides.
(c) Any area of the geomembrane sheets where adhesive accidentally
spilled and caused damage greater than 10% of the original thickness,
must be patched as above with at least 15 cm (6 inches) of
geomembrane extending beyond the affected areas.
(d) Any area of the geomembrane sheets where puncture holes are observed
must be patched as above with at least 15 cm (6 inches) of
geomembrane extending beyond the affected areas.
(e) Note that with the above three repair items (b, c, and d) it is not
practical to use a seaming board beneath the geomembrane. However,
a piece of the liner material can be used for added support under
the liner, if needed, even if the hole must be enlarged to insert the
piece before the patch is made. This added piece is left there
indefinitely. In either situation, additional care is necessary to
insure a proper bond.
(f) Sandbags used to resist wind uplift stresses may to be placed on the
seamed areas in accordance with customary installation practice or as
prescribed in the contract specifications.
(g) Cross sections of the completed seams are shown in Figure lO.ll(a-c).
150
-------
(a) Air lance test.
(b) Pick test.
Figure 10.10. Photographs of air lance and pick testing of completed seam.
151
-------
Figure 10.11(a).
Cross sections of CSPE-R seams fabricated by the
chemical adhesive seaming method showing left
side of completed seam.
I
Figure 10.11(b).
Cross sections of CSPE-R seams fabricated by the
chemical adhesive seaming method showing center
side of completed seam.
152
-------
Figure 10.11(c).
Cross sections of CSPE-R seams fabricated by the
chemical adhesive seaming method showing right
side of completed seam.
10.6 UNUSUAL CONDITIONS
This section is written to give insight into conditions which go beyond
the general description just presented.
(a) High winds, or gusts of wind, are always problematic for liners.
After deploying the geomembrane, the panels should be adequately
ballasted, e.g., with sandbags. The actual seaming operation,
however, may require the removal of some of the ballast leaving the
windward edge vulnerable to wind uplift forces. If possible, proper
orientation of the overlap might be helpful. Otherwise, additional
labor may be required to only remove sandbags immediately in front
of the seaming operation. The liner must be cleaned of any dirt and
moisture left behind after sandbag removal. They are then to be
replaced behind the completed seaming operation.
153
-------
(b) Patches are invariably necessary to make at locations where
destructive test samples are removed or where seams are shown to
fail nondestructive testing. These patches must extend a minimum of
15 cm (6 inches) beyond the outer limits of the area to be repaired.
Since a seaming board cannot be used in these areas, additional care
is necessary. Sometimes excess pieces of geomembrane material which
are left in place, are positioned beneath the area to be seamed.
(c) Details around sumps, pipes and other appurtenances are perhaps the
most demanding locations in an entire facility to properly seam.
Also due to their typical locations being at low points of the
containment facility's design, these areas inherently operate under
larger hydraulic heads. Should a defect from improper seaming occur
in such a location leakage rates and its associated adverse impacts
are heightened. Therefore, extreme care should be exercised in
ensuring seam integrity in these often difficult to reach locations.
The adhesive should be placed symmetrically on both liners to be
joined which may be difficult for external and internal edges and
particularly at corners. Hand and finger pressure is needed in
tight locations.
(d) This section was written for material temperatures that range
between 0°C (32'F) and 50°C (122'F). This is the temperature range
that is generally recognized as being acceptable for seaming without
taking special precautions.
For sheet temperatures below 0°C (32°F), shielding, preheating,
different chemical compounds and/or a slower seaming rate may be
required. More frequent seam testing and precautions to prevent
thawing subgrade (previously discussed) may have to be taken.
Sharp, frozen subgrade should be avoided or perhaps a geotextile
used to eliminate point pressure damage potential.
For sheet temperatures above 50°C (122'F), shielding and rate of
seaming should be adjusted. More frequent destructive seam testing
may have to be taken.
I
154
-------
FIELD NOTES:
155
-------
FIELD NOTES:
I
156
-------
SECTION 11
EMERGING TECHNOLOGIES FOR GEOMEMBRANE SEAMING
Selected geomembrane sheet seaming methods which are not widely used at
the present time are discussed in this section. These include ultrasonic
seams, electrical conduction bonding and magnetic induction bonding methods.
The physical principles of each of these techniques are discussed, as
well as their current degree of development and implementation. The potential
advantages and disadvantages of the methods are also discussed.
11.1 ULTRASONIC SEAMS
Ultrasonic methods are used by various industries in a variety of ways.
These include product cleaning, thickness gauging, nondestructive flaw
detection, hardness testing, exotic machining, emulsification, sewing,
biological cell disruption, bonding of quite dissimilar materials (as in the
microelectronics area) and, of course, joining plastics. The technique is
well advanced and fully implemented in areas other than geomembrane seaming.
In ultrasonic seaming of thermoplastics, an intense local vibration is
induced at the material interface by means of a piezoelectric, or
magnetostrictive, driven horn, see Figure 11.1. The exact mechanism of the
bonding is not completely understood but it involves friction-driven melting
(at least locally) of the plastic and subsequent solidification and bonding.
Pressure is usually applied to the interface during the bond's formation. It
is also suggested that the breaking of non-resin materials (e.g, oxides) at
the interface may be inherent to the bonding process. The frequencies of
vibration in ultrasonic welding are usually in the tens of kilohertz range.
The weld time is typically very short; on the order of a few seconds.
Figure 11.2 is a schematic drawing of the ultrasonic seaming process for
seaming of geomembrane sheets. The sheet material to be seamed is fed between
the two rollers; between the sheets is located the ultrasonic horn. The horn
vibrates longitudinally at approximately 40,000 Hz (cycles/sec) and works in
the squeeze roller nip areas directly against the two surfaces to be joined.
The vibrational peak-to-peak amplitude is about 0.038 mm (0.0015 in.). The
vibrating action works with the frictional characteristics of the material to
produce the heat for melting and bonding the geomembrane. Materials with
higher frictional coefficients produce heat more rapidly. Knurled surfaces
are usually incorporated into the working areas of the horn to better engage
the material, to disrupt any surface contaminants, to concentrate the energy
and to provide for mixing of the molten polymer just as the sheets are
entering the squeeze portions of the rollers. The unit can seam thermoplastic
157
-------
Plastic Sheets
Horn
Anvil
^^vj
Metal Sheets
Lr"
(a)
Ib)
Figure 11.1. Schematic diagrams of ultrasonic welding of
plastic (and metal) sheets.
Figure 11.2. Schematic diagram of rollers, ultrasonic horn
and geomembrane sheets in the ultrasonic seaming
process. The method is called the "Ultrascanner"
by the developers.
158
-------
to 1.5 meters/min. (3-5 feet/minute). Shear and peel values of the completed
seams are reported to be as good as with traditional seaming techniques.
11.2 ELECTRICAL CONDUCTION SEAMING
In the electrical conduction seaming technique for plastics, electric
current is passed through wires embedded in (or placed between) the vicinity
of the parts to be joined. The temperature of the wires rises via ohmic
heating and the heat is transferred to the plastic which melts in the vicinity
of the wires. Upon solidifying, the parts are joined. Pressure is usually
applied, either physically, or indirectly by differences in thermal expansion
of the parts. Both ac and dc currents have been used. Welding times are
typically the same as those common in the geomembrane heat fusion techniques,
for it is essentially a thermal technique. This particular seaming method is
widely used in the natural gas plastic pipeline area and is usually called the
"electro-fusion" technique. Figure 11.3 gives a schematic diagram of the
electro-fusion process which indicates that certain properties are measured in
real-welding time, and fed back to the control panel to readjust and optimize
welding conditions.
Initial tests on this type of seaming of geomembranes were on a 1.5 mm
(60 mils) HOPE geomembrane. Stainless steel wires were braided around a 0.6
cm (1/4 inch) diameter HOPE core. Figure 11.4 shows a sketch of the assembly.
A force was applied normal to the sheets with the braided wire between.
Electrical current (ac) of 5-10 amperes was passed through the wires. The
wires heat due to ohmic effects and melt the core and the adjacent sheet
material. The current was stopped after a prescribed time and the material
subsequently solidified, thereby bonding the sheets together. Under the
present experimental circumstances, maximum weld lengths of about 1 meter
(3 feet) can be made with a single application of the current electrodes.
To date the electrical conduction technique has not been used to field
seam geomembranes and is currently in an experimental stage.
11.3 MAGNETIC INDUCTION SEAMING
In electromagnetic induction seaming, a conductor and/or hysteretic
material (in the form of wires, particles, strips, etc.) is placed at the
interface to be joined. A non-contacting, induction coil containing high
frequency electric current passes over the area to be seamed. The
time-varying magnetic field caused by the current in the coil induces eddy
currents and/or hysteresis loss in the embedded materials. Hence the area is
heated, melts, solidifies and bonding takes place. Pressure is usually
applied to the interface. Frequencies generally range from 3-7 MHz and 80-320
KHz, depending on the particular application. A wide variety of plastic
assembly and sealing applications have been performed. The electromagnetic
induction method has been mentioned briefly in the natural gas pipeline
literature, but no details are available as to its use.
159
-------
Figure 11.3. Schematic diagram of an electrofusion pipe coupling process.
I
CORE
VOLTAGE
0SOURCE
CURRENT
Figure 11.4. Schematic diagram of the electrical conduction
method of joining geomembranes.
160
-------
Figure 11.5 is a schematic diagram of the fabrication process of
electromagnetic induction seaming for geomembranes. An HOPE sheet of 0.945
g/cm3 density and 1.5 mm (60 mils) thickness was used in the tests. The
braided core, made by the same process as described for the electrical
conduction method is placed between the two sheets and force is applied normal
to the sheet. An electromagnetic coil carrying high frequency alternating
current of about 200 KHz is passed directly over the braided core. No contact
whatsoever is made between the electromagnetic coil and the sheet. The coil
is about 0.6 cm (1/4 inch) to 1.2 cm (1/2 inch) above the top geomembrane
sheet. Eddy currents are induced in the embedded braided wire by the
time-varying magnetic field. This results in ohmic heating which melts the
core and a certain amount of the adjacent sheet material. After the coil has
passed, the eddy currents cease and the material solidifies and bonds the
sheets together. Rates of about 0.3 m/min. (1.0 ft/min.) have been achieved.
Preliminary results of mechanical testing of the seams give about 90% of sheet
value for shear but are very poor in peel. By optimization of the welding
parameters, this situation may improve.
To date the magnetic induction technique has not been used to field seam
geomembranes and is currently in an experimental stage.
HIGH FREQUENCY
ALTERNATING CURRENT
CORE
•PRESSURE
Figure 11.5. Schematic diagram of the magnetic induction method
of joining geomembranes.
161
-------
FIELD NOTES:
162
-------
SECTION 12
REFERENCES
1. Frobel, R. K., "Methods of Constructing and Evaluating Geomembrane
Seams," Proc. Conf. on Geomembranes, Denver, CO., 1984,
IFAI, pp. 359-364.
2. Lord, A. E. Jr., Koerner, R. M. and Crawford, R. B., "Nondestructive
Testing Techniques to Assess Geomembrane Seam Quality," Proc.
Mgmt. of Uncontrolled Haz. Waste Sites, Washington, DC, 1986,
HMCRI, pp. 272-276.
3. Overmann, L. K., "Nondestructive Seam Testing: CQC Perspectives,"
Proc. on the Seaming of Geosynthetics, Journal of Geotextiles
and Geomembranes, Elsevier Appl. Sci. Pub. Ltd., Vol., No. 4-6,
1990, pp. 415-430.
4. Richardson, G. N., "Nondestructive Seam Testing: CQA Perspectives,"
Proc. on the Seaming of Geosynthetics, Journal of Geotextiles
and Geomembrane, Elsevier Appl. Sci. Pub. Ltd., Vol. 9, No. 4-6,
1990, pp. 445-450.
5. Haxo, Henry E. Jr., and L. C. Kamp, "Destructive Testing of Geomembrane
Seams: Shear and Peel Testing of Seam Strength," Proc. on the
Seaming of Geosynthetics, Journal of Geotextiles and Geomembranes,
Elsevier Appl. Sci. Pub. Ltd., Vol. 9, No. 4-6, 1990, pp. 369-396.
6. Peggs, Ian D., "Destructive Testing of Polyethylene Geomembrane Seams:
Various Methods to Evaluate Seam Strength," Proc. on the Seaming
of Geosynthetics, Journal of Geotextiles and Geomembranes, Elsevier
Appl. Sci. Pub. Ltd., Vol. 9, No. 4-6, 1990, pp. 405-414.
7. Matrecon, Inc., "Lining of Waste Containment and Other Impoundment
Facilities," EPA/600/2-88/052, NTIS PB89-129670, Sept. 1988.
8. U.S. EPA Technical Guidance Document, "Construction Quality Assurance
for Hazardous Waste Land Disposal Facilities," EPA/530-SW-86-031,
NTIS PB87-132825, Oct. 1986.
9. Haxo, H. E. Jr., "Quality Assurance of Geomembranes Used as Linings for
Hazardous Waste Containment," Journal of Geotextiles and
Geomembranes, Vol. 3, No. 4, 1986, pp. 225-248.
163
-------
10. Apse, J. I., "Polyethylene Resins for Geomembrane Applications,"
Proc. on Aging and Durability of Geosynthetics, R. M. Koerner,
Ed., Elsevier Appl. Sci. Pub. Ltd., 1989, pp. 159-176.
11. ASTM, Proposed Document for Task Committee D-4000 on Plastic Liners,
June, 1989.
12. Koerner, R. M., Designing with Geosynthetics, 2nd Edition, Prentice
Hall Publ. Co., Englewood Cliffs, NO, 1990.
13. Koerner, G. R. and Bove, J. A., "Construction Quality Assurance of
HOPE Geomembrane Installations," Proc. Geosynthetics '89,
San Diego, CA., IFAI, pp. 70-83.
14. ASTM D 4439, "Terminology for Geosynthetics," American Society for
Testing and Materials, Philadelphia, PA.
I
164
-------
FIELD NOTES:
165
-------
FIELD NOTES:
166
-------
SECTION 13
GLOSSARY OF TERMS
Air Lance - A commonly used nondestructive test method performed with a stream
of air forced through a nozzle at the end of a hollow metal tube to
determine seam continuity and tightness of relatively thin, flexible
geomembranes.
Adhesive - A chemical system used in the bonding of geomembranes. The
adhesive residue results in an additional element in the seamed area.
(Manufacturers and installers should be consulted for the various types
of adhesives used with specific geomembranes.)
Anvil - In hot wedge seaming of geomembranes, the anvil is the wedge of metal
above and below which the sheets to be joined must pass. The temperature
controllers and thermocouples of most hot wedge devices are located
within the anvil.
Bodied Chemical Fusion Agent - A chemical fluid containing a portion of the
parent geomembrane that, after the application of pressure and after the
passage of a certain amount of time, results in the chemical fusion of
two essentially similar geomembrane sheets, leaving behind only that
portion of the parent material. (Manufacturers and installers should be
consulted for the various types of chemical fluids used with specific
geomembranes in order to inform workers and inspectors.)
Buffing - An inaccurate term often used to describe the grinding of
polyethylene geomembranes to remove surface oxides and waxes in
preparation of extrusion seaming.
Chemical-Adhesive Fusion Agent - A chemical fluid that may or may not contain
a portion of the parent geomembrane and an adhesive that, after the
application of pressure and after passage of a certain amount of time,
results in the chemical fusion of two geomembrane sheets, leaving behind
an adhesive layer that is dissimilar from the parent liner material.
(Manufacturers and installers should be consulted for the various types
of chemical fluids used with specific geomembrane to inform workers and
inspectors.)
Chemical Fusion - The chemically-induced reorganization in the polymeric
structure of the surface of a polymer geomembrane that, after the
application of pressure and the passage of a certain amount of time,
results in the chemical fusion of two essentially similar geomembrane
sheets being permanently joined together.
167
-------
Chemical Fusion Agent - A chemical fluid that, after the application of the
passage of a certain amount of time, results in the chemical fusion of
two essentially similar geomembrane sheets without any other polymeric or
adhesive additives. (Manufacturers and installers should be consulted
for the various types of chemical fusion agents used with specific
geomembranes to inform workers and inspectors.)
Chlorinated Polyethylene (CPE) - Family of polymers produced by the
chemical reaction of chlorine with polyethylene. The resultant polymers
presently contain 25-45% chlorine by weight and 0-25% crystallinity.
Chlorinated Polyethylene-Reinforced (CPE-R) -Sheets of CPE with an
encapsulated fabric reinforcement layer, called a "scrim".
Chlorosulfonated Polyethylene (CSPE) - Family of polymers produced by the
reaction of polyethylene with chlorine and sulphur dioxide. Present
polymers contain 23.5 to 43% chlorine and 1.0 to 1.4% sulphur. A "low
water absorption" grade is identified as significantly different from
standard grades.
Chlorosulfonated Polyethylene-Reinforced (CSPE-R) - Sheets of CSPE with an
encapsulated fabric reinforcement layer, called a "scrim".
Construction Quality Assurance (CQA) - A planned system of activities
whose purpose is to provide an evaluation of the completed liner
and initiate corrective action where necessary.
Construction Quality Control (CQC) - Actions that provide a means of
monitoring and measuring the quality of the product as it is being
installed.
Crystal Structure - The geometrical arrangement of the molecules that occupy
the space lattice of the crystalline portion of a polymer.
Curing - The strength gain over time of a chemically fused, bodied chemically
fused, or chemical adhesive geomembrane seam due primarily to evaporation
of solvents or crosslinking of the organic phase of the mixture.
Curing Time - The time required for full curing as indicated by no further
increase in strength over time.
Destructive Tests - Tests performed on geomembrane samples cut out of a field
installation or test strip to verify specification performance
requirements, e.g., shear and peel tests of geomembrane seams during
which the specimens are destroyed.
Drive Rollers - Knurled or rubber rollers which grip the geomembrane sheets
via applied pressure and propel the seaming device at a controlled rate
of travel.
168
-------
Dwell Time - The time required for a chemical fusion, bodied chemical fusion
or adhesive seam to take its initial "tack", enabling the two opposing
geomembranes to be joined together.
Environmental Stress Crack (ESC) - see also Stress Crack - External or
internal stress propagation in a plastic caused by environmental
conditions which are usually chemical or thermal in nature.
Ethylene Interpolymer Alloy (EIA)- A blend of ethylene vinyl acetate and
polyvinyl chloride resulting in a thermoplastic elastomer.
Ethylene Interpolymer Alloy-Reinforced (EIA-R) - Sheets of EIA with an
encapsulated fabric reinforcement layer.
Extrudate - The molten polymer which is emitted from an extruder during
seaming using either extrusion fillet or extrusion flat methods. The
polymer is initially in the form of a ribbon, rod, bead or pellets.
Extrusion Seams - A seam between two geomembrane sheets achieved by heat-
extruding a polymer material between or over the overlap areas followed
by the application of pressure.
Factory Seams - The seaming of geomembrane rolls together in a factory to make
large panels to reduce the number of field seams.
Field Seams - The seaming of geomembrane rolls or panels together in the field
making a continuous liner system.
Fishmouth - The uneven mating of two geomembranes to be joined wherein the
upper sheet has excessive length that prevents it from being bonded flat
to the lower sheet. The resultant opening is often referred to as a
"fishmouth".
Flashing - The molten extrudate or sheet material which is extruded beyond
the die edge or molten edge, also called "squeeze-out".
Flexible Member Liner (FML) - Synonymous term for geomembrane.
Flood Coating - The generous application of a bodied chemical compound, or
chemical adhesive compound to protect exposed yarns in scrim reinforced
geomembranes.
Geomembrane - An essentially impermeable membrane used as a solid or liquid
barrier. Synonymous term for flexible membrane liner (FML).
Geotextile - Any permeable textile used with foundation, soil, rock,
earth, or any other geotechnical engineering-related material as an
integral part of a human-made project, structure, or system.
Grinding - The removal of oxide layers and waxes from the surface of a
polyethylene sheet in preparation of extrusion fillet or extrusion flat
seaming.
169
-------
Gun - Synonymous term for hand held extrusion fillet device or hand held
hot air device.
High Density Polyethylene (HOPE) - A polymer prepared by low-pressure
polymerization of ethylene as the principal monomer and having the
characteristics of ASTM D1348 Type III and IV polyethylene. Such
polymer resins have density greater than or equal to 0.941 g/cc
as noted in ASTM D1248.
Hook Blade - A shielded knife blade confined in such a way that the blade
cuts upward or is drawn toward the person doing the cutting to avoid
damage to underlying sheets.
Horn - The vibrating device used with ultrasonic seaming which vibrates at
high frequency causing friction and a subsequent melting of the surfaces
that it contacts.
Initial Reaction Time - Dwell time.
Medium Density Polyethylene (HOPE) - A polymer prepared by low-pressure
polymerization of ethylene as the principal monomer and having the
characteristics of ASTM D1348 Type II polyethylene. Such polymer resins
have density less than 0.941 g/cc as noted in ASTM D1248.
Mouse - Synonymous term for hot wedge, or hot shoe, seaming device.
Nondestructive Test - A test method which does not require the removal of
samples from, nor damage to, the installed liner system. The evaluation
is done in an in-situ manner. The results do not indicate the seam's
mechanical strength.
Oxide Layer - The reacting of atmospheric oxygen with the surface of the
polymer sheet.
Pinholes - Very small imperfections in sheet or seamed geomembranes which may
allow for escape of the contained liquid.
Plasticizer - A material, generally an organic liquid, incorporated in a
plastic or rubber formulation to soften the resin polymer and improve
flexibility, ductility and extensibility.
Polyethylene (PE) - A semi crystalline thermoplastic'polymer made by
polymerizing ethylene and other co-monomer(s).
Polymer - A carbon based organic chemical material formed by the chemical
reaction of monomers having either the same or different chemical
structures. Plastics, rubbers and textile fibers are all relatively high
molecular weight polymers.
170
-------
Polyvlnyl Chloride (PVC) - A non-crystalline thermoplastic polymer composition
prepared from polymerized vinyl monomer by blending with one or more low
or non-volatile plastisizers made by polymerizing vinyl chlorine monomer.
Pressure Rollers - Rollers accompanying a seaming technique which apply
pressure to the opposing geomembrane sheets to be joined. They closely
follow the actual melting process and are self-contained within the
seaming device.
Puckering - A heat related sign of localized strain caused by improper
seaming using extrusion or fusion methods. It often occurs on the bottom
of the lower geomembrane and in the shape of a shallow inverted "V".
Quality Assurance - See construction quality assurance.
Quality Control - See construction quality control.
Scrim Designation - The weight and number of yarns of fabric reinforcement
per inch of length and width, e.g, a 10 X 10 scrim has 10 yarns per inch
in both the machine and cross machine directions.
Scrim (or Fabric) Reinforcement - The fabric reinforcement layer used with
some geomembranes for the purpose of increased strength and dimensional
stability.
Sealant - A viscous chemical used to seal the exposed edges of scrim
reinforced geomembranes. (Manufacturers and installers should be
consulted for the various types of sealant used with specific
geomembranes).
Seaming Boards - Smooth wooden planks placed beneath the area to be seamed
to provide a uniform resistance to applied roller pressure in the
fabrication of seams.
Shielded Blade - A knife within a housing which protects the blade from
being used in an open fashion, i.e., a protected knife.
Squeeze-Out -See "flashing".
Solvent, Bodied Solvent and Solvent Adhesive - See Chemical Fusion, Bodied
Chemical Fusion and Chemical Adhesive.
Stress Crack - ASTH D1693 - An external or internal rupture in a plastic
caused by tensile stress less than its short-time mechanical strength.
Stress Crack - ASTN D883 - An external or internal crack in a plastic caused
by tensile stresses less than its short-time mechanical strength.
Note: The development of such cracks is frequently accelerated by the
environmental to which the plastic is exposed. The stresses which cause
cracking may be present internally or externally or may be combinations
of these stresses.
171
-------
Tack - Stickiness.
Tensiometer - A device containing a set of opposing grips used to place a
geomembrane seam in tension for evaluating its strength in shear or in
peel.
Test Strips - Trial sections of seamed geomembranes used (1) to establish
machine setting of temperature, pressure and travel rate for a specific
geomembrane under a specific set of atmospheric conditions for machine-
assisted seaming and (2) to establish methods and materials for chemical
and chemical adhesive seams under a specific set of atmospheric
conditions.
Test Welds - See "test strips".
Thermal Fusion - The temporary, thermally-induced reorganization in the
polymeric make-up of the surface of a polymer geomembrane that, after the
application of pressure and the passage of a certain amount of time,
results in the two geomembranes being permanently joined together.
Thermoplastic Polymer - A polymer that can be heated to a softening point,
shaped by pressure, and cooled to retain that shape. The process can be
done repeatedly.
Thermoset Polymer - A polymer that can be heated to a softening point,
shaped by pressure, and, if desired, removed from the hot mold without
cooling. The process cannot be repeated since the polymer can not be
resoftened by the application of heat.
Vacuum Box - A commonly used type of nondestructive test method which
develops a vacuum in a localized region of an geomembrane seam in order
to evaluate the seam's tightness and suitability.
Very Low Density Polyethylene (VLDPE) - A linear polymer of ethylene with
other alpha-olefins with a density of 0.900 to 0.910.
Waxes - The low molecular weight components of some polyethylene compounds
which migrate to the surface over time and must be removed by grinding
(for HOPE) or be mixed into the melt zone using thermal seaming methods.
Wicking - The phenomenon of liquid transmission within the fabric yarns of
reinforced geomembranes via capillary action.
172
-------
FIELD NOTES:
173
-------
FIELD NOTES:
174
•6 U.S. GOVERNMENT PRINTING OFFICE: 1991 548-187/25637
------- |