United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/020 Aug. 1986
SERA Project Summary
Grouting Techniques in Bottom
Sealing of Hazardous Waste
Sites
James H. May, Robert J. Larson, Philip G. Malone, John A. Boa, Jr., and Dennis
L Bean
Bottom sealing of hazardous waste
sites involves the injection or insertion
of an inert impermeable and continuous
horizontal barrier in soil below the
source of contamination. This type of
containment stragegy could be used in
conjunction with other technology such
as slurry walls, capping, and counter-
pumping to insure that contaminants
do not move from the site into surround-
ing soil or ground water. The objectives
of this project were to determine which
types of available grouts would be
unreactive with hazardous wastes and
how effective direct injection or jet
grouting techniques would be in form-
ing a grout barrier. The effectiveness of
a complete barrier was not evaluated.
Grout formulations used in this study
were acrylate, 30% silicate, 50% sil-
icate, urethane, and portland cement.
These grouts were tested to determine
their ability to set and remain intact in
the presence of twelve different simu-
lated waste solutions (acids, bases,
fuels, and organic solvents), that could
occur at hazardous waste sites. The
grouts which showed the greatest abil-
ity to set were the two inorganic-based
formulations: sodium silicate and Type
1 Portland cement. Acrylate grout set in
six out of twelve simulated wastes, but
the urethane grout tested did not set in
any of the simulated wastes.
When grout samples set in water
environments were exposed to the same
twelve solutions for 20 days, all except
the portland cement product showed
some swelling or shrinkage. Of the
chemical grouts, sodium silicate and
acrylate exhibited the best durability.
In a small-scale 2 m x 4 m (6.56 ft x
13.12 ft) test bed of medium sand,
neither silicate nor acrylate grout in-
jected into a grid-like pattern of bore-
holes formed a continuous horizontal
seal. The grout bulbs either did not
coalesce (silicate) or were displaced
after injection (acrylate). In a large-
scale test using sodium silicate grout
injected at a depth of 2.44 m (8 ft) in
fine sand, the shapes of the grout bulbs
could not be controlled well enough to
produce a seal, and grout shrinkage
caused root holes to remain unsealed.
Chemical grouting as employed in this
test did not produce a continuous
bottom seal.
Tests of jet grouting were undertaken
in natural (in-place) loess, compacted
silt, and medium sand at a depth of 1.67
m (5.5 ft), using three holes spaced on
1.52 m (5 ft) centers. The water jet
system succeeded in producing useful
cavities in all media but the shape and
size of the cavities could not be con-
trolled with sufficient precision in the
loess or silt to produce a continuous
bottom seal when the cavities were
grouted. The less cohesive sand washed
out more evenly and the grouted cav-
ities overlapped to form a continuous
barrier layer.
These studies indicated that present
grouting techniques do not permit close
enough control to assure that a bottom-
seal will be formed under the conditions
tested.
This Project Summary was developed
by EPA '5 Hazardous Waste Engineering
Research Laboratory, Cincinnati, OH,
to announce key findings of the research
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project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Grouting has been used in construction
for over a century to add strength to earth
materials or to control water movement.
Grouting involves the pressure injection
of suspensions or solutions that set or
harden to fill voids and cement earth
materials together. Both the grout formu-
lation selected for injection and the
technique used for placement are im-
portant for grout to produce the desired
benefits.
Grouting has been used to emplace a
subsurface barrier in remedial action
involving radioactive waste and has been
indicated as a potentially useful tech-
nique for neutralizing, immobilizing, or
containing toxic wastes. Proposals for
using grout have involved shallow, low-
pressure injection to consolidate contam-
inated soil; injection i nto waste to provide
for solidification or in-situ treatment and
injection for sealing soil around the site to
form a barrier to lateral or vertical con-
taminant migration. Projects have also
been undertaken where waste was used
as a filler in the grout. In all applications of
grout at waste sites, two properties are
critical:
1. The grout must set or harden in
contact with waste components.
2. The grout must not deteriorate in
the presence of the waste during
normal temperature or moisture
cycles occurring within the expect-
ed lifetime of the grouted structure.
Two types of grouts, chemical (or
solution) grouts and particulate (or sus-
pension) grouts are available for use in
producing subsurface barriers. Chemical
grouts are solutions that react to produce
a gel or polymer that fills the pore space.
The solutions typically have a low initial
viscosity that increases rapidly during
setting. Particulate grouts are suspen-
sions of fine-grained solids that move
between the particles of the medium
being grouted. The setting of particulate
grouts may be produced by a chemical
reaction or by the flocculation of the
dispersed solid. The grout types differ in
their injectability and their effectiveness
in producing a durable seal or adding
strength to the grouted medium. In ap-
plications where grout is to form a barrier
in geologic media, the grout must be
easily injectable (have low viscosity) and
must produce a decrease in permeability.
Grouts typically are injected using
pumps and mixers. For effective applica-
tion it is also necessary that the grout.
1. Have a set time that can be regu-
lated.
2. Be reasonably non-corrosive to
mixers and pumps.
3. Be formulated from materials that
are low in toxicity.
After a grout has been selected, a
technique for grout application must be
identified. Chemical grouts are generally
low-viscosity liquids that can be directly
pumped into porous media. The grain-
size of the sediment that can be injected
depends on the time available for injection
and the viscosity of the grout. Generally,
particulate (suspension) grouts cannot be
injected into sediments finer than med-
ium sand. In finer grain-size material,
chemical (solution) grouts must be used
unless a technique for washing out a
cavity is applied. Hydraulic excavation of
a cavity for placing grout is usually
referred to as jet grouting.
Jet grouting is done using a wide array
of techniques. A water jet can be operated
in a water-filled cavity or in a concentri-
cally-placed air jet. A water jet can also be
operated in an air-filled pressurized cav-
ity. A variety of fluids can be employed in
jet grouting, including clean water, ben-
tonite clay suspensions, or portland ce-
ment suspensions. Cuttings are air-lifted
or pumped to the surface. Air or water
pressure is maintained in the cavity to
prevent collapse of the roof or side walls.
The research reported here consists of
three related phases:
1. Screening and selection of grouts .
for bottom sealing of hazardous \
wastes.
2. Evaluation of chemical grout tech-
nology for producing a continuous
bottom seal.
3. Evaluation of jet grouting technol-
ogy for producing a continuous
bottom seal.
The three phases, grout selection,
chemical grout evaluation, and jet grout
evaluation, cpmbined demonstrate the
currently available technology and the
limitations involved in attempting to
bottom-seal using current grouting tech-
niques. A full-scale barrier test was not
undertaken.
Selection of Grouts for Bottom
Sealing
Four types of grout (five formulations)
selected for testing included silicate (30%
and 50-60%), acrylate, urethane, and
Portland cement. These were tested for
compatibility with twelve simulated
wastes prepared as shown in Table 1.
The effects of wastes on the grout set
times were determined by mixing sep-
arate samples of each prepared grout
with an equal volume of each simulated
waste solution. Setting of the urethane
grout tested was completely inhibited by
every simulated waste tested. Acids,
bases, oxidizers, and copper sulfate in-
hibited the acrylate grout. Sodium hy-
droxide solution (10%) inhibited the 30%
sodium silicate grout, and it slowed the
setting of 5O% sodium silicate grout.
Ammonium chloride slowed the set of
Portland cement but produced a flash set
with sodium silicate. Copper sulfate pro-
duced a flash set with both portland
cement and sodium silicate.
Table 1.
Characteristics of Waste Test Solutions Used
Waste Component
Potassium chromate
Hydrochloric acid
Ammonium hydroxide
Sodium hydroxide
Ammonium chloride
Copper sulfate
Benzene
Gasoline
Oil
Phenol
Toluene
Trichloroethylene
Character of
Waste
Strong oxidizer
Inorganic acid
Base
Base
Salt
Salt
Cyclic hydrocarbon
Hydrocarbon mixture
Hydrocarbon mixture
Substituted benzene
Substituted benzene
Halogenated hydrocarbon
Concentration of
Waste
10%
10%
10%
10%
10%
10%
Saturated
Saturated
Saturated
Saturated
Saturated
Saturated
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Chemical Grout Injection
Small-scale injection tests of acrylate
and silicate grouts were conducted by
injecting each grout into a 1 meter deep.
layer of clean medium-grained sand in a
separate test bed. No impervious grout
layer was formed in either the silicate or
the acrylate test beds.
Several problems related to field condi-
tions were observed during excavation of
the grouted sand beds:
(a) The grouted sand masses were
often highly assymetrical and large
gaps existed between grout bulbs.
(b) Voids larger than those between
sand grains (root holes or rootlet
holes) were not sealed with grout.
The insides of the voids were usual-
ly coated with grout, but the holes
were still open.
(c) Coarse-grained filter sand used at
the bottom of the injection hole was
often completely uncemented with
no evidence of grouting although
the fine-grained sand around the
filter sand was completely cement-
ed.
Jet Grouting
Jet grouting is a technique for excavat-
ing a cavity in the subsurface using a
high-pressure fluid jet. The jetting fluid
can be water, water with entrained air, or
a water/bentonite suspension. After the
cavity has been excavated, grout is in-
troduced to fill the cavity and form an
impermeable mass. Jet grouting has the
advantage that a wide variety of grouts
can be used, even particulate grouts, like
bentonite or bentonite/cement.
The jetting system used in this study
consisted of a high-pressure positive
displacement piston pump that delivers
cutting fluid to a downhole jetting nozzle
that can be directed from the surface. The
grout used was a standard portland
cement/bentonite grout. Fluorescein,
rhodamine, or methylene blue were used
to color the pods so they could be easily
identified. The three different soils tested
were (1) an undisturbed porous inter-
locked loess, (2) compacted silt, and (3) a
compacted mortar sand.
In all cases cavities could be produced,
but cutting was so irregular in the silt and
loess that no continuous seal was pro-
duced. The sand washed out more evenly
and the grouted cavities overlapped to
form a continuous layer.
Conclusions
None of the commonly used chemical
grouts examined in this study exhibited
all of the necessary characteristics for
success. Injection grouting tests using
sodium silicate demonstrated the follow-
ing points:
(a) The shape of the chemical grout
bulbs cannot be controlled due to
inhomogeneity in the soil being
grouted. The irregular shapes and
positions of the grout bulbs make it
difficult to form a continuous barrier
by injecting grout bulbs that coa-
lesce.
(b) Large holes in soil masses (root
holes) will not adequately seal ifthe
chemical grout undergoes shrink-
age (syneresis).
(c) Coarse-grained soils and fine-
grained soils in the grouted area
may require different chemical
grouts to assure that the chemical
grout can penetrate, and after pene-
tration will not shrink and pull away
from the coarse material.
Jet grouting offers several advantages
over injection grouting in the proposed
application:
(a) Jet grouting is effective in a wide
variety of geologic media (such as
silt or fine sand or mixed silt and
sand) that cannot be grouted in any
other way.
(b) Cutting a cavity allows elimination
of inhomogeneities in soil (such as
root holes, channel fillings, sand
plugs, etc.) when grout is injected.
(c) A wide variety of grouts (chemical,
particulate, or mixed) can be used in
jet grouting. The large variety of
grouts available makes it possible
to select material that is chemically
non-reactive and-durable in soils
contaminated with hazardous
waste chemicals.
(d) Waste/grout interaction during
grout setting is minimized in jet
grouting.
The following major difficulties were
observed with jet grouting:
(a) The size and shape of the cavity
produced in jetting could not be
determined without special sensing
equipment mounted in the jetting
head.
(b) Jet grouting required specialized
equipment, usually beyond that
available from normal drilling and
grouting contractors.
(c) The cutting fluid needed to be
recycled or disposed of as a possible
hazardous waste.
(d) Jet grouting in the form evaluated
in this study required set-up and
clean-up times that were far longer
than those required for chemical
injection grouting.
(e) The grout selected for injection
needed to be thoroughly tested to
assure that it would remain as an
impermeable barrier.
Recommendations
The results obtained in this investiga-
tion indicate that chemical grouts, as
currently used, are poorly suited to bottom
sealing. Many of the problems with
chemical grouts noted in bottom sealing
tests are identical to deficiencies noted in
construction applications. As advances
are made in grout technology in construc-
tion, the possible applications to bottom
sealing should be evaluated. Jet grouting
appears to offer the greater promise of
being further developed to obtain a satis-
factory bottom grouting procedure.
Future research needs include the
development of down-hole techniques
for monitoring cavity geometry in jet
grouting and the development of rapid
techniques for inserting a jet and pro-
ducing a cavity without drilling a hole and
setting a casing. Bottom sealing in soft
soil possibly could be done from a soil
probe (inste'ad of drilling), with great
savings of time.
The full report was submitted in fulfill-
ment of Interagency Agreement DW-
96930581-01-3 by the U.S. Army Engi-
neer Waterways Experiment Station
under sponsorship of the U.S. Environ-
mental Protection Agency. This report
covers a period from June 1982 to June
1985, and work was completed as of
September 1985.
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James H. May, Robert J. Larson, Philip G. Malone, John A. Boa, and Dennis L.
Bean are with USAE Waterways Experiment Station, Vicksburg, MS 39180-
0631.
Herbert R. Pahren is the EPA Project Officer (see below).
The complete report, entitled "Grouting Techniques in Bottom Sealing of
Hazardous Waste Sites," (Order No. PB 86-158 664/A S; Cost: $11.95, subject
to change} will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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EPA/600/S2-86/020
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