United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/023 June 1987
&EPA Project Summary
The Block Displacement
Method Field
Demonstration and
Specifications
Thomas P. Brunsing
The Block Displacement technique
has been developed as a remedial
action method for isolating large tracks
of ground contaminated by hazardous
waste. The technique places a low
permeability barrier around and under
a large block of contaminated earth.
The Block Displacement process is
composed of separate bottom barrier
and perimeter barrier construction
processes. The bottom barrier con-
struction is accomplished by propagat-
ing horizontal separations from a series
of injection wells. A soil-bentonite
slurry is pumped into these wells at low
pressure, opening the separation and
forming a barrier. In the process the
ground is displaced upward by an
amount corresponding to the thickness
of the final barrier placed. The perime-
ter barrier is constructed by one of
various means including slurry wall, jet
grouting, or drill notch and blast. The
perimeter barrier is constructed prior to
the bottom if necessary to induce a
favorable in-situ stress state.
The technique was demonstrated at
Whitehouse, FL where a block of earth
60 ft in diameter and 25 ft deep was
lifted. Horizontal fractures were
extended from seven injection holes to
form the bottom barrier. The block was
displaced upward as much as 12 in. by
the injection of approximately 2,000 ft3
of bentonite slurry. Upward displace-
ment was monitored by standard sur-
vey techniques during the lifting pro-
cess. After displacement was
completed, a topographic survey was
conducted and the quality of the
bottom barrier was assessed by core
drilling.
This Project Summary was devel-
oped by EPA's Hazardous Waste
Engineering Research Labaoratory,
Cincinnati, OH, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Block Displacement is a method for
vertically lifting a large mass of earth.
The technique produces a fixed under-
ground physical barrier around and
beneath the earth mass. The barrier is
formed by pumping slurry, composed of
a soil bentonite and water mixture, into
a series of notched injection holes. The
resulting barrier completely isolates the
earth mass.
The process is illustrated in Figure 1
for isolating a chemical waste site. In-
ground pollution is contained by inhib-
iting ground-water migration through the
contaminated zone. The barrier material
should be compatible with in situ soil and
ground-water chemistry.
A bottom barrier is formed when
lenticular separations extending from
horizontal notches at the base of injec-
tion holes coalesce into a larger sepa-
ration beneath the ground being isolated.
Continued pumping of slurry under
pressure produces a large uplift force
against the bottom of the block and
results in vertical displacement propor-
tional to the volume of slurry pumped.
A perimeter barrier is constructed with
the bottom barrier either prior to, during,
or following bottom barrier construction.
The perimeter barrier can be constructed
including slurry wall, vibrating beam.
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Groundwater Level
Lowered
Barrier
Positive Seal Through
Injected Bentonite
Mixture
Figure 1. Block displacement barrier in place.
dynamic fracturing, or jet groutingtech-
niques. If constructed prior to bottom
separation, the perimeter barrier can be
used to enhance the horizontal stress
field for the purpose of maintaining the
horizontal orientation of the propagating
bottom separations. A perimeter separa-
tion would first be constructed and then
surcharged to increase the horizontal
stress field in the formation. A surcharge
is additional pressure transmitted to the
fluid slurry in the perimeter separation
either by raising the slurry fluid level
above ground level or by placing a seal
in the perimeter separation and pressur-
izing the slurry below the seal.
The Block Displacement method can
be used to increase the width of an
initially thin perimeter barrier such as
might be constructed by vibrating beam,
dynamic fracturing, or jet grouting
techniques. To increase perimeter width
by means of the block lift, the thin
perimeter must be constructed on a slight
angle off vertical prior to a substantial
portion of the lift. The slight angle off
vertical tapers inward toward the block
center. Upward displacement of the block
resulting from injection along the bottom
barrier will then increase the initial
thickness of the perimeter separation.
Construction of the bottom barrier
proceeds in four phases:
Bottom Barrier
1. Formation of notches at the base
of the injection holes
2. Initial bottom separation of the
notched holes
3. Propagation of the local separa-
tions at each injection point coa-
lescing into a single larger bottom
separation
4. Generation of a complete bottom
barrier by controlled vertical dis-
placement of the earth mass using
low pressure slurry injection into
the horizontal separation.
Each of these phases is carried out
through control and monitoring of slurry
pressure, slurry flow rate, total volume
injected, and slurry composition. Defor-
mation and vertical displacement of the
isolated soil is also monitored.
The notching operation (Phase 1)
requires a high-pressure rotating jet at
the base of the injection hole. The jetting
slurry is designed to optimize notch
erosion, to remove cuttings, and to
minimize leak-off into the soil. A
mechanical notching tool can be used in
lieu of the jet notching tool, but the
maximum notch diameter achievable will
be reduced. A large notch diameter is
desired to reduce fracture initiation
pressure and to reduce the tendency for
propagating separations to turn upward
due to unfavorable in situ stress condi-
tions.
The initiation of bottom separation
(Phase 2} requires a slurry pressure, P0,
at the separation defined by.
Po = prgh + AP
where p, = the average earth mass den-
sity of the soil overlaying the
notching operation
g = the gravitation constant
AP = the pressure in excess of the
overburden
h = the depth of the bottom
separation
The pressure in excess of overburden,
AP, is a function of soil properties, notch
diameter, slurry properties and the speed
of the operation. The strength of a
material being fractured is classically
measured by its fracture toughness. The
pressure required to initiate propagation
is the pressure required to open a
sufficiently wide gap at the tip of the
notch to allow the slurry to flow into the
separation. The gap width is dependent
on the gel strength of the slurry. The
tendency for the slurry to leak off into
the soil and form filter cake at the tip
of the notch complicates this process and
increases the required initiation pres-
sure.
Separation coalescence (Phase 3]
occurs by adding slurry volume and by
gradually increasing the gel strength and
viscosity of the slurry. Slurry pressure
required to propagate the horizontal
separation will decrease during this
phase due to the increased area ovet
which it is acting. The viscosity of the
slurry serves to limit flow in one specific
direction, thereby avoiding undesirable
channeling of slurry material. The higher
viscosity increases pressure drop al
distances from the injection holes,
reducing the pressure available foi
fracturing. This pressure/distance rela-
tionship causes the separations tc
maintain a generally circular shape in the
horizontal plane.
Vertical displacement (Phase 4) utlizes
the maximum capacity of the pumping
equipment to inject a slurry with higr
solids content to form the final barrier
When the perimeter barrier separatior
is constructed prior to displacing the
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ground, the required injection pressure
is dependent on the overburden weight,
system geometry, shear resistance in the
perimeter and slurry pressure drop
across the bottom separation.
The final thickness of the bottom
barrier can be controlled to any dimen-
sion, from a few inches to several feet.
The desired thickness depends on the
isolation required by the structure or soil
mass being isolated.
Field Demonstration
Site Description
A demonstration of the Block Displace-
ment technique was conducted at a site
adjacent to the Whitehouse Oil pits in
Whitehouse, FL The Whitehouse site
was selected from a list of 114 top priority
EPA superfund sites.
The site was flat and composed of
marine sediments of silty sand in excess
of 100 ft overlaying limestone bedrock.
The silty sand appeared to be sufficiently
stratified to be compatible with Block
Displacement. Ground-water level in the
area varies from 2 to 5 ft, and local drillers
indicated that a thick hardpan layer
existed at a depth of approximately 20
ft. •
Three exploratory holes were drilled
and continuously sampled. The soil
profile was categorized, and the standard
penetration resistance was recorded in
all holes. Hardpan was encountered in
all three holes at approximately 10-ft
depth and continued to between 20 and
25 ft underlaid by unconsolidated brown
sand. The contact between hardpan and
brown sand below was a gradual tran-
sition of interbedded layers and lenses
of the two soils.
The transition zone between hardpan
and underlying brown sand appeared to
be a suitable medium for inducing bottom
fracture. A block diameter of 60 ft and
depth of 23 ft were selected based on
this geology.
Construction
The field operation involved three
distinct operations:
• An explosive blast in three adjacent
test holes to determine perimeter
fracture performance
• Preparation of the block by drilling and
slotting 32 perimeter holes, and
drilling and casing seven slurry injec-
tion holes
• Fracturing both the bottom and the
perimenter, and lifting the block.
Perimeter Test Blast
Before commencing with the block
perimeter and injection hole drilling,
three test holes were drilled to a depth
of 27 ft at a 14 degree angle off vertical.
The three holes were of 6-in. diameter
and spaced at 3-ft and 6-ft intervals along
a straight line. They were drilled in an
area apart from the proposed test block.
This drilling was done to gain experience
in angled drilling with the mobile rig, to
experiment with hole slotting tools, and
to use these holes to conduct an exper-
imental blast for joining the slot tips. The
hole spacing and explosive charge load
would determine the ultimate number of
block perimeter holes required. Twenty-
six feet of 50-grain/ft Prima-cord™*
explosive were placed to within 1 ft of
the top of each hole, and 10 ft were
overlapped at the bottom to give this
portion of each hole a 100-grain/ft load.
The cord was capped at the bottom of
each hole using a special cap insertion
tool. Post-blast inspection showed that
the fractures between the 3-ft spaced
holes clearly joined; and that the 6-ft
spaced holes had their slots extended far
enough to join but not in a straight line,
thus making verification difficult.
Injection Hole Drilling
Seven 23-ft deep injection holes were
to be cased with 6-in. PVC pipe, and
hence required a larger bit for drilling.
An 8-in. bit was fabricated, and with the
exception of encountering occasional
tree roots, the drilling went smoothly.
PVC pipe in 25-ft lengths was installed
i n each hole so that the last 2 ft protruded
above ground. Each hole was also bottom
grouted using Portland cement to ensure
a reasonable casing seaJ. Two cubic feet
of grout were placed in each hole
displacing the drilling mud. The PVC
casing was then pressed through the wet
grout using the drill rig downhaul. The
cement was later drilled through to earth,
and the casings were temporarily
capped.
Perimeter Hole Drilling
The experience gained during test hole
drilling proved very helpful for the
perimeter hole drilling. At each of the 32
hole locations, the drill rig was positioned
•Mention of trade names or comercial products does
not constitute endorsement or recommendation for
use.
on the block perimeter and tilted to the
desired 14 degree angle by extending the
appropriate hydraulic stabilizer jack
inside the block. Subsequent measure-
ment indicated that the off vertical
anglevaried from 12 to 14 degrees
around the block. The 6-in. drill bit was
used, and five to seven holes were
completed each day. A fresh batch of 10
percent bentonite by weight m ud was left
in each hole to ensure against hole
collapse
Perimeter Slotting
For the perimeter slotting operation, a
pile driver was brought to the site and
two new and different slotting tools.were
fabricated. Because of the large surface
area and general geometry of the disc
slotter, the impact force required to drive
it was so great that the pipe bent severely
before the tool reached the bottom of the
first hole. A second tool with a reduced
area, diamond-shaped slotter was fab-
ricated using a single length pipe. The
thickness of the slot blades was also
reduced by half for this tool. Using the
modified diamond slotter, the pile driver
heads were angled at 14 degrees off
vertical. The pile driver delivered 700- to
1,400-ft-lb blows to the slotting tool,
typically driving the tool 6 in./blpw. All
32 perimeter holes were slotted in just
over 3 days.
Perimeter Fracture
In preparation for the perimeter frac-
ture blasting, a 5-ft long, 18-in. diameter
"sona tube" (tubular heavy gauge card-
board cement form) was placed on-end
over each perimeter hole, as shown in
Figure 2. Each tube was then filled with
a very heavy barite (specific gravity of
>2.0) mud, which acted as a surcharge
to prevent mud loss during the blast, and
to force the mud in each perimeter hole
out into the separation created by the
blast.
With this accomplished, the explosive
charges were loaded into each hole and
fired. A,detectable perimeter fracture
appeared to run around almost,the entire
circumference of the block at the surface.
A piece of spring steel was used to probe
the fracture to verify hole connection.
This device confirmed that most perime-
ter holes did join down to a depth of
several feet, beyond which the spring
steel could not penetrate the fracture.
The blast-induced fracture appeared
continuous.
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Figure 2. Surcharged perimeter holes ready for explosive blast.
Bottom Notching and Fracture
The bottom notching technique
employed a high-pressure, slurry jet
oriented horizontally and rotated at the
bottom of the hole to erode a pancake
shaped notch. Initially a 2-percent
bentonite slurry was jetted in a slurry
medium in all seven injection holes
yielding notches 2 ft in diameter. During
the first attempt to create a fracture, high
pressure was required to induce slurry
flow. This indicated the need for larger
notches. Renotching of the holes first to
a 4-ft diameter and finally to a 6-ft
diameter was required to create the
bottom fracture.
Block Lift
A mud distribution manifold was
fabricated for both fracturing and lift
operations. A 3-in. diameter inlet port
was connected to the outlet of the mud
pump, and each valved 2-in. outlet port
was connected to an injection hole
casing. Each casing had a pressure
gauge installed as a means of monitoring
injection pressure and as an aid in
detecting connections with other holes.
Although the manifold permitted mud
injection into any number of the seven
holes simultaneously, the pumping was
usually confined to one of three holes
at a time. The hole selected to receive
the mud was determined by measure-
ments of lift at certain points on the block
using the engineer's level set up outside
the block. When lift was observed at an
injection point, the mud was then
directed to a different injection hole in
an attempt to lift the entire block surface
as evenly as possible. This process was
continued until each injection hole was
lifted between 1/32 and 1/16 in. during
mud injection. Separation coalescence
between injection holes was observed
after approximately 500 gal. of slurry
were pumped into the central injection
hole. Once lift was detected, the injection
slurry was modified by adding local soil
to add weight and reduce cost. The added
material was surface excavated, silty
sand that acted as an aggregate in the
bentonite and water matrix. After several
days of pumping, primarily into the
central injection hole, some lift had been
detected nearly everywhere.
Summary of Test Results
Displacement of the block was mon-
itored by recording the change in eleva-
tion of 16 fixed rods. Elevations were
read through a surveyor's level located
50 ft outside of the block perimeter.
Additional survey poi nts beyond the block
boundary were monitored during a
portion of the lift operation to verify that
no lift was occurring outside of the
perimeter. Survey points 0 through 6
correspond to rods located approximately
3 ft from the injection holes. The remain-
ing nine survey points, 3p through 30p,
correspond to rods located just inside the
perimeter. These survey point numbers
correspond to the closest hole numbered
progressively from 1 to 32 in a counter-
clockwise direction around the perime-
ter.
A total of approximately 2,000 ft3 of
bentonite slurry was injected during the
block lift operation. A daily tabulation of
slurry injected during the lift operation
was maintained by counting the number
of 1 -1 /2 yd3 batches of slurry mixed and
verifying this count with a daily bag count
of the bentonite used.
Data from surface topographic surveys
and from accumulated daily lift records
were combined to give the two profiles
of the final block position shown in Figure
3. In total, the block was displaced
upward in excess of 12 in. at its highest
point and tilted approximately one degree
from horizontal. A crescent shaped
portion of the block outside of injection
hole No. 3 was sheared free of the lifting
block and did not move appreciably. The
entire remaining portion of the perimeter
lagged behind the inner portion of the
block, lifting only 3 to 6 in.
Tap roots as large as 24 in. in diameter
were found at approximate 6-ft intervals
extending from roughly 5 ft below the
ground surface to the upper boundary of
the hardpan layer. In addition, perimeter
fractures filled with gelled slurry
extended down only a few feet before
becoming indistinguishable hairline
fractures.
Thin-walled tube soil samples were
taken 4 weeks after stopping slurry
pumping to determine the integrity of the
bottom seal. Obtaining undisturbed soil
samples of the soft slurry material
bounded by hardpan on top and uncon-
solidated sand beneath was difficult. In
eight attempts, three acceptable samples
were obtained. Sample No. 8 shown in
Figure 4 indicated that a well defined
boundary of separation between injected
clay slurry and the overlapping native
sand had formed.
Conclusions
The Block Displacement demonstra-
tion provided three distinct technical
conclusions:
• The bottom barrier construction com-
ponent of the process is viable and
has been demonstrated.
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Non-Lifting
Section of
Block \
i i 7»W
Ground
Water
Elevation
24ft
-Soft-
Injection Holes
Displaced
Block
12 in.
jn _] L_ Bottom Slurry Barrier
Section A-A'
Perimeter
"— 3 w.
idated material. Slurry mix, pumping and
distributing equipment demonstrated
that the slurry designs used can be
adequately mixed and placed in the field.
Lift monitoring using standard survey
equipment was quite adequate for deter-
mining performance and as feedback for
correcting slurry injection during the
lifting operation. Adequate correlation
was obtained between slurry injected
and ground volume displaced.
The full report was submitted in
fulfillment of Contract No. 68-03-3113,
Task 37-2 by JRB Associates under the
sponsorship of the U.S. Environmental
Protection Agency.
5 in. —J
Figure 3. Final block displacement.
in.
Section B-B'
• The drill, slot and blast perimeter
barrier construction technique applied
as part of the total isolation process
was unsatisfactory and should not be
considered for Block Displacement
application.
• Construction materials, equipment
and procedures for implementing the
Block Displacement process were
evaluated and refined sufficiently to
be considered for field application
under geologic conditions similar to
those at the demonstration site.
The bottom barrier construction tech-
nique, which required repeated modifi-
cation to notching and sealing tech-
niques, ultimately performed quite
consistently. Drilling, notching, separa-
tion propagation, and block lift were all
adequately demonstrated. Surface dis-
placements, core samples and lift volume
versus slurry volume correlations all
support this conclusion. Subsequent
coring data, lift monitoring data and
independently derived conclusions from
interpretation of ground penetrating
radar records indicate at least 80 percent
of the underlying area defined by the
design perimeter was covered by bottom
barrier material.
The drill, slot and blast perimeter
separation technique did not produce a
sufficiently smooth continuous fracture
to allow the perimeter surfaces to fully
override each other during the displace-
ment process. Performance of this
perimeter separation technique in the
more consolidated hardpan is uncertain,
as post lift perimeter mapping could not
extend down into the hardpan region.
Alternate, more direct perimeter con-
struction techniques such as slurry wall
or vibrating beam construction would be
more appropriate in unconsolidated
ground.
Slurry jetting in a compressed air
stabilizing medium proved adequate as
a bottom notching method in unconsol-
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Bentonite
Slurry
Barrier
Bentonite
Slurry
Barrier
Figure 4. Test core from hole No. 8.
Thomas P. Brunsing is with Foster-Miller, Inc., Waltham, MA 02254.
Walter E. Grube, Jr. is the EPA Project Officer (see below).
The complete report, entitled "The Block Displacement Method Field
Demonstration and Specifications." (Order No. PB 87-170 338/AS; Cost:
$18.95, 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
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EPA/600/S2-87/023
OC00329 PS
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