To print brochure, click herethen click the print button in your browser.
INQUIP Associates, Inc., a speciality geotechnical
contractor, traces its roots back to the beginning of the slurry trench
technology in 1950 on the Terminal Island Project. This was the first trench
ever excavated under bentonite slurry for an industrial application. The
company was founded in 1977 to continue and further develop the activity
of the groundwater control division of Industrial Engineering and Equipment
Corporation, founded by Mr. Charles H. Toll, one of the pioneers in the
development of the slurry trench method. Mr. Toll was instrumental in the
promotion and construction of economical underground seepage barriers,
including the Terminal Island Project.
INQUIP's main
activity from its creation to the early eighties was related to the installation
of soil-bentonite cutoff barriers and liners. In order to utilize the wide
experience of its management team and to be able to satisfy more efficiently
the needs of its clients, INQUIP expanded its product line to other geotechnical
services. This carefully controlled growth process is expected to continue
in the future. Many of the speciality techniques offered by INQUIP have
applications for the control and mitigation of pollution associated with
landfills and waste management facilities.
INQUIP offers
capabilities for the installation of:
All types of underground seepage barriers Cast-in-place or precast slurry walls for support of excavations Deep soil mixing Leachate collection systems Liners Pressure and jet grouting
INQUIP has
experience with federal and state regulations governing health and safety
for remediation work on the hazardous and toxic sites.
INQUIP's major
goal is to provide excellent service to its clients and to maintain a high
level of quality construction. Only qualified, technically capable field
managers oversee site construction. The company management strongly believes
that close understanding and cooperation with the owner and the engineer
are essential in resolving technical difficulties and achieving high performance.
INQUIP looks forward to working closely with its clients for the successful
completion of their projects.
Slurry Trench Method of Excavation
Bentonite slurry has been used to stabilize
trenches under excavation since 1950. This technique, referred to as the
slurry trench method, has enabled excavation of deep, narrow vertical trenches
in soils which cannot otherwise stand unsupported without using shoring
and/or dewatering, and particularly in soils beneath the groundwater table.
During excavation, the vertical walls are supported by keeping the trench
filled with bentonite slurry. The hydrostatic thrust of the slurry is the
primary stabilizing force supporting the saturated soils. Slurry fabricated
with biodegradable polymers instead of bentonite has been used to stabilize
trenches for specific applications.
The slurry trench method of excavation is used for the following types
of construction:
INQUIP specializes in construction
using all of the above techniques throughout the United States and Canada,
and occasionally internationally, both as a contractor and subcontractor.
In some cases INQUIP works directly with the general contractor, owner
or engineer by providing expertise and specialized equipment.
INQUIP is available to discuss
your project and to supply for your consideration specific application
information and budget costs. Please contact any of our regional offices
for more details.
Pollution Control Projects
INQUIP has considerable experience
working on hazardous and toxic waste sites. These projects either involve
the remediation or closure of the sites and may use one or more of our
specialty geotechnical techniques. Slurry cutoff walls are often used to
contain contaminated groundwater and prevent the horizontal migration of
leachates, or prevent the infiltration clean groundwater. Collection/extraction
trenches constructed by the Bio-Polymer technique are used to collect and
extract leachate. Other INQUIPtechniques such
as grouting, HDPE curtain walls, and stabilization have also been successful
used to contain pollution.
Proper planning and engineering are a requirement on all pollution containment
projects. The chemistry of the leachate may effect the cutoff wall backfill
mix and the bentonite slurry and these are normally tested prior to construction
for compatilility. Groundwater flow may change after the installation of
a slurry wall, so groundwater modeling is often used to evaluate groundwater
control schemes. With proper planning, containment is often the most economical
and lowest risk approach for pollution control.
Combinations of geotechnical techniques
are commonly used to minimize costs and optimize the construction of a
pollution containment. The combination of a slurry cutoff wall with groundwater
wells or collection trenches, capped with a barrier membrane, is often
the most acceptable and economical method for groundwater containment.
When space is limited, groundwater barriers and extraction can be combined
in a single trench fitted with a HDPE curtain wall, aggregate, and extraction
wells or piping. On difficult sites, problem soils or sludges may be stabilized
to reduce the generation of leachates, and then contained with a slurry
cutoff wall and less extensive groundwater controls.
INQUIP specializes
in creating innovative and cost effective systems and combinations of techniques
for pollution containment.
INQUIP is
available to discuss your project and to provide for your consideration
specific constructability information and budget costs. Please contact
any of our regional offices for moreinformation.
Soil-Bentonite Cutoff Wall
Soil-Bentonite(S-B) cutoff wallsare excavated
in a continuous manner under bentonite slurry. The cutoff is keyed in most
cases into an impervious stratum or bedrock. Impervious backfill is placed
into the trench, displacing the slurry to form the completed cutoff. The
backfill includes soils excavated from the trench and/or borrow materials.
These materials are blended with slurry to yield a homogeneous mixture
with a consistency corresponding to a 3 to 6 inch slump. The low permeability
of the cutoff results primarily from the native clay in the backfill mixture.
If not enough clay is present, bentonite is added to the mixture. Secondarily,
low permeability results from the development of a bentonite "filter
cake" on each wall of the trench and from slurry entering the voids
of the formation adjacent to the trench.
Akey factor in selecting the S-B cutoff over other
alternate systems is economics. In many cases this method offers substantial
savings over conventional systems such as sheet piling, grouting, clay
core trenches, well points or reservoir liners. Sometimes the S-B cutoff
is combined with other systems to obtain optimum efficiency. S-B cutoffs
are most economical where excavation depth is in the range of standard
construction equipment, such as backhoes (including those modified to reach
depths in excess of 80 feet), and when the excavated material can be used
to backfill the trench. They have proven to be effective seepage barriers.
Permeabilities can be achieved from lxl0-6 to less than lxl0-7
cm per sec.
S-B cutoff walls have been used for many years as permanent
cutoffs through and below dams and as temporary cutoffs to minimize the
flow of groundwater into large excavations. They are also used for containment
at hazardous and toxic waste sites to minimize the outward migration of
leachate or the inflow of groundwater when leachate collection or extraction
systems are provided as part of the remediation program.
Soil-Cement-Bentonite Cutoff Wall
Soil-Cement Bentonite (S-C-B) cutoff walls
are a more recent development in slurry trenching technology. S-C-B cutoff
walls attempt to combine low permeability of S-B cutoff walls in a material
with a moderate strength. This technique may be advantageous on some sites
since the trench soil may be reused in the backfill, thus minimizing disposal
volume. S-C-B cutoff walls may be divided into at least three types: S-C-B
cutoff walls, plastic concrete cutoff walls, and cutoff walls constructed
by insitu soil mixing which incorporates bentonite and cement. S-C-B cutoff
walls are generally shallow (less than 50 ft. deep) and constructed nearly
identical to S-B cutoff walls but cement is added as well as bentonite
to the soils. Normally native soils are mixed into the backfill and the
typical permeability is in the 10-6 cm/sec range. S-C-B cutoff
walls usually have an unconfined compressive strength (UCS) of 5 to 250
psi.
When deeper trenches are required, plastic concrete cutoffs may be the
optimum choice for the slurry wall backfill. Plastic concrete is a weak
concrete (UCS=500 to 1500 psi) with a small amount of bentonite, and may
use sand and fly ash instead of soil for the base ingredient in the backfill.
In deeper trenches, a more controllable and better engineered material
is required to prevent the accumulation of sediments on the bottom of the
trench and potentially windows at cold joints. Plastic concrete is often
the material choice in very deep cutoff walls or in cases where some consolidation
of the adjacent soils is expected after the cutoff wall installation. Plastic
concrete cutoff walls are usually constructed in alternating panels so
the joints can be excavated between panels to create a strong seal. Plastic
concrete ingredients are usually mixed in a ready mix plant or other similar
equipment that can carefully control proportions.
Deep soil mixed (DSM) cutoff walls typically use a mixture of cement and
bentonite as admixtures. DSM walls have similar strength and permeability
to S-C-B slurry walls. With DSM walls all ingredients must be added as
a fluid so workability of the S-C-B grout is critical. The amount of admixture
in DSM wall is also limited because of workability limitations of the grout.
In DSM walls the grout also serves as drilling fluid and therefore, soil
resistance and spoil generation are also related to workability.
The presence of cement creates strength, but also challenges. All S-C-B
materials must be sampled during construction. Except for the plastic concrete,
after setting up in the trench the materials are too soft to core drill
and too hard to push sample without creating microscopic cracks in the
sample and producing erroneous results. The potential for cold joints and
windows is greater in S-C-B cutoff walls, and therefore quality control
measures must be more exacting. Other ingredients may be used in place
of cement or bentonite to create slightly different properties or reduce
costs including: attapulgite clay, flyash, slag cement, gypsum, and many
other similar materials.
INQUIP installed the largest to date S-C-B cutoff wall (725,000 square
feet) in 1997 in California to control seepage through river levees.
Cement-Bentonite Cutoff Wall
Cement-Bentonite (C-B) slurry trench cutoff walls utilize
a bentonite slurry containing cement to stabilize the trench during the
excavation phase. After completion of the excavation, the cement causes
the slurry to harden to a strength comparable to that of a stiff clay,
thereby eliminating the need for trench backfilling. The cement-bentonite
slurry contains no aggregate other than some suspended soil particles from
the excavation process, The bentonite provides the media to keep the cement
in suspension until initial set occurs.
Strength and plasticity of the hardened cement-bentonite
slurry will vary, depending mostly on the cement/water ratio and the type
of cement, with higher strengths having lower plasticity. Mixes can be
designed to achieve unconfined compressive strength from 5 psi to well
over 20 psi at 28 days.
Additives, including setting retarders, can be incorporated
in the mixture to achieve certain operating characteristics, or for economy.
For example, flyash is sometimes used as a filler to increase the density
of the slurry and to reduce the cement content. The permeability of C-B
cutoff walls depends on the proportions of bentonite, cement and flyash
used in the mix. Permeability can normally be achieved in the range of
10-5 to 10-6 cm per sec. Lower permeabilities can
be achieved if required.
Some of the primary reasons for selecting C-B cutoff walls
instead of soil-bentonite cutoff walls are:
Design requirement for strength of the
backfill. Potential for trench instability due to soft and loose soil zones
or adjacent surcharges. The panel method of excavation can be employed where these conditions
are critical. Site conditions restricting the working area and preventing the preparation
of the S-B backfill mixture alongside the trench. Unavailable or costly materials suitable for soil-bentonite backfill.
INQUIP has experience in the installation of C-B cutoff walls since 1977,
and has access to advances in mix technology through license agreements.
Concrete Slurry Walls
Concrete Slurry walls are slurry walls
constructed to carry structural loading. These slurry walls are backfilled
with steel reinforcing and concrete, and used as retaining walls, basement
walls, or as the walls of tunnels especially when groundwater presents
a problem for construction. There are at least two kinds of structural
walls; diaphragm (or cast-in- place) walls and precast walls. Concrete
slurry walls are usually excavated under bentonite slurry in alternating
panels. The length of the panel depends on site conditions and the length
of the excavating tool, typically a slurry clam bucket. In addition to
excavating and backfilling, concrete slurry wall panel must be treated
to ensure the integrity of the joints and the quality of the concreting
operation.
Diaphragm walls are the most common concrete slurry walls. After excavating,
the panels of a diaphragm wall must be "desanded" to remove excess
sand that accumulates on the bottom or is suspended in the slurry. Next,
prefabricated steel reinforcing or "rebar cages" are lowered
to the panel. The rebar cages may also support future structural or utility
connections using "knockouts" that are pre-set in the wall. Next,
the panel is filled with a high slump concrete which is placed in the wall
through tremie pipes, to prevent segregation of the wet concrete. After
the primary panels are set, the secondary panels are created between the
primary panels to complete the wall. Control of verticality and careful
cleaning of the concrete is important to the quality of the seal between
panels. Sometimes steel beams (soldier piles) are used to better reinforce
the connection between the primary and secondary panels, this is referred
to as the "soldier pile tremie concrete" (SPTC) method. The appearance
of the completed wall is a direct reflection of the soil excavation. In
some cases, the surface of the wall can be covered with paint or shotcrete
for a better visual effect.
Precast concrete slurry walls are built
utilizing precast concrete panels, either reinforced or prestressed, which
are inserted into slurry filled trenches. The precast elements are usually
placed in a special C-B slurry to seal the joints. When settlement is critical,
the bottom of the precast panel can be set into tremie concrete. The main
advantage of the precast walls is the ability to have an architectural
appearance of the completed wall.
Concrete slurry walls are often used as the walls for a variety of deep
excavations where the space is intended to be permanently useable. Sometimes
concrete slurry walls are used to accelerate the construction of large
buildings using the "top-down" construction approach where the
basement and the upper floor are constructed simultaneously after a concrete
slurry wall is installed to support the basic structure. Also, the "cover
and cut" construction developed in Europe, has enabled construction
of underground structures in congested areas in a more expedient and efficient
manner. With this method, cast-in-place or precast slurry walls are placed
as the perimeter finished walls of the underground structure. The top cover
is then poured on grade, leaving access openings through which the mass
excavation under the top cover and between the slurry walls is performed.
This method can minimize the disturbance of traffic and other above ground
activities. Such activities are restored while the remaining work takes
place below the cover slab. Concrete slurry walls are also used to support
bridge abutments and other structures which must carry vertical loadings
and horizontal earth loads.
Bio-Polymer Drain & Recharge Trenches
Bio-Polymer (B-P) trenches are installed
for drainage, leachate collection, or recharge systems where in-the-dry
installation methods are not feasible or where cost savings can be realized.
B-P trenches differ from normal slurry trenches in two ways. First, the
slurry used to support the trench walls during excavation is made from
a biodegradable material such as guar gum or polymer. Second, the trench
backfill is a pervious material such as permeable sand or drain rock. After
completion of the backfill, the slurry filling the voids of the filter
material is treated to allow it to biodegrade or break down. It is then
flushed out of the granular material. Drains installed by the bio-polymer
method are usually deeper than 15 to 20 feet and have achieved depths of
nearly 70 feet. They are used when the groundwater or soil conditions would
result in an unstable situation without a trench shoring system, or where
contaminated groundwater exists. In the latter case, the B-P trench method
eliminates the need for dewatering, thereby greatly reducing the necessity
for costly treatment or disposal of contaminated water from dewatering
operations.
The B-P methods have been used on numerous polluted sites to reduce the
cost of remediation. B-P trenches have been used to install pump and treat
systems, air sparging trenches, groundwater collection and reinjection
galleries and groundwater barriers. B-P drains also have uses in civil
engineering including applications such as toe or chimney drains for earthen
dams, groundwater diversion trenches, and dewatering for slope stabilization.
The construction of complex drainage trenches (with multiple liners, pipes,
and aggregate) can be made cost-effective with the Bio-Polymer trench technique,
however there are a number of construction considerations which must be
resolved. First, all structures placed in a B-P trench must be weighted
to sink into place through the slurry. Standard manufacturer's recommendations
are available for placing some types of pipes under water or slurry. Fabrics
must be designed not to trap the polymer in its weave. In general needle
punch fabrics are not recommended, whereas woven fabrics are better suited.
HDPE liners can be placed in the trench using special frames, rollers,
and other construction aids. However it is not possible to weld joints
under the slurry. Often a complex design can be simplified by substituting
well casings for manholes and flexible corrugated slotted drain pipe for
rigid pipe.
A soil-bentonite or cement-bentonite cutoff wall can be used as a containment
device in conjunction with a B-P drainage or recharge trench to eliminate
the necessity of a HDPE liner in the B-P trench.
Reactive Barriers-Funnel and Gate®
Reactive Barriers are in-ground or insitu
treatment systems that use specialty engineered media or bio-organisms
to clean contaminated soil and groundwater. Reactive barriers can be permeable
or impermeable and may use media such as iron filings, carbon, peat moss,
and bacteria. Reactive barriers can be used to treat a variety of organic
compounds and heavy metal contamination. The significant advantage of reactive
barriers is that they can be effective without pumping, mass excavation
of contaminated soil, above-ground treatment facilities or off site disposal.
The installation of reactive materials can be subdivided into two categories:
1) one-time (buried) installations, and 2) replaceable (cassette) installations.
The one-time installation is the case where the reactive media is simply
buried in a trench. The primary design variable is the width of the reactive
media and the volume required for the lifetime of the installation. Cassette
installations require a permanent underground structure such as a slotted
tank, large diameter manhole, or similar receiving structure. The cassette
system anticipates changing the reactive media or using a sequential treatment
system. Piping valves, and connections can be necessary with cassette systems
so the installations are usually more complicated and costly.
The efficiency of reactive barrier installations can be significantly improved
by controlling the flow of groundwater through the media. The funnel and
gate installations often use slurry cutoff walls as wingwalls to funnel
groundwater into a permeable reactive barrier or gate. Slurry cutoff walls
can also be used to encircle contamination and permit a single vessel of
permeable reactive media inside the containment to economically treat a
controlled volume of groundwater. Special bacteria or high carbon fly ash
can be added to the soil-bentonite slurry cutoff wall to create an impermeable
reactive barrier.
The construction of reactive barriers for buried installations can be made
more economical using proven slurry trench and soil mixing methods. For
permeable reactive barriers, the Bio-polymer drain method can be used to
install the media without the need for dewatering, sheeting or shoring.
Injecting reactive media via soil mixing can treat soil contamination in
one application without excavation or other invasive methods.
INQUIP installed the first commercial permeable reactive barrier in
1994. This funnel and gate used cement bentonite and soil cement bentonite
slurry walls to funnel ground water through an iron filings gate on a congested
industrial site in California. INQUIP also installed the first commercial
impermeable reactive barrier in 1996. A soil- bentonite slurry wall was
installed containing a high carbon fly ash additive in the backfill around
a sludge landfill in Michigan.
Insitu Soil Mixing
Insitu soil mixing is a geotechnical technique
that has numerous cost effective applications for civil/infrastructure
projects and environmental remediation. Typically, large mixing augers
(3 to 12 ft. diameter or more) or modified excavator tools are used to
mix soil or sludge with a cement grout or other reagents to improve their
properties or treat buried contamination. Insitu soil mixing has the significant
advantage of soil treatment without excavation, dewatering or shoring.
Soil mixing has the capability to go to depths greater than 10 feet. Insitu
soil stabilization has been used to build retaining walls, cutoff walls,
and other foundation systems. Insitu treatments can be used to volatilize
or oxidize contaminants, stabilize sludges, mix and inject biological or
reactive media and to implement a wide variety of other insitu treatments.
The design of insitu soil mixing projects requires a comprehensive understanding
of the site conditions and the goals of the construction. Usually a pre-construction
laboratory testing program is enacted to establish performance criteria,
material requirements and budget cost. The testing may be used to determine
workability, volume increase, strength, permeability, leachate chemistry,
or biological characteristics of the treated soils. A pilot program, or
field test can also be implemented, if required, to better determine the
specifics of the project. A well designed laboratory performance and/or
pilot program will usually provide an accurate prediction of project performance.
INQUIP was one of the first contractors to use modified caisson-type
equipment (12 ft. diameter) for soil stabilization. INQUIP has also used
modified excavators to stabilize soft soils and wastes. This line of work
has been a natural extension of our normal slurry trench work of mixing
soils and grout. Our staff has been involved in many of the largest and
innovative soil mixing projects including combinations of soil mixing with
soil vapor extraction, zero valent metals, and biological agents. New concepts
in soil mixing include the use of special soil mixing patterns, combinations
of soil mixing with slurry cutoff walls and special mixing patterns to
create a composite soil structure for retaining walls and foundations.
Soil mixing is an extremely flexible geotechnical technique which has a
variety of applications for contaminated soil treatment, as well as for
soil improvement. Insitu soil mixing continues to evolve and suggest new
methods for soil improvement and treatments.
If you have an immediate or future application for any
of our specialty construction techniques, please
contact us. If you need additional information please e-mail us at:
info@inquip.com,
or call one of our offices.
All types of underground seepage barriers
