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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