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USACE / NAVFAC / AFCESA / NASA UFGS-02 35 27 (April 2006)
--------------------------
Preparing Activity:
USACE Replacing without change
UFGS-02262 (August 2004)
GUIDE SPECIFICATION FOR CONSTRUCTION
References are in agreement with UMRL dated 1 April 2006
Section Table of Contents
SECTION 02 35 27
SOIL-BENTONITE (S-B) SLURRY TRENCH
04/06
PART 1 GENERAL
1.1 REFERENCES
1.2 MEASUREMENT AND PAYMENT
1.2.1 Measurement
1.2.2 Payment
1.3 DEFINITIONS
1.3.1 Slurry Trench
1.3.2 Slurry Method of Excavation
1.3.3 Bentonite
1.3.4 Slurry
1.3.5 Soil Bentonite (S-B) Backfill
1.3.6 Ground Water Level
1.3.7 Working Surface
1.3.8 Confining Stratum
1.4 PERFORMANCE REQUIREMENTS
1.5 SUBMITTALS
1.6 QUALIFICATIONS
1.6.1 Contractor
1.6.2 Slurry Trench Specialist
1.6.3 Slurry Trench Excavation Equipment Operator
1.7 DELIVERY, STORAGE, AND HANDLING
1.8 GEOTECHNICAL SITE CONDITIONS
1.8.1 Exploratory Borings
1.8.2 Subsurface Conditions
1.8.3 Ground Water
1.8.4 [Embankment Conditions]
1.9 QUALITY CONTROL TESTING
1.9.1 Bentonite Tests
1.9.2 Water Tests
1.9.3 Backfill Material Tests
1.9.4 Slurry Properties
1.9.5 S-B Backfill Tests
1.9.6 Samples of Confining Stratum
PART 2 PRODUCTS
2.1 MATERIALS
2.1.1 Bentonite
2.1.2 Water
2.1.3 Backfill Material
2.2 EQUIPMENT
2.2.1 Trench Excavation Equipment
2.2.2 Slurry Mixing and Cleaning Equipment
2.2.3 Field Laboratory Equipment
2.3 BENTONITE SLURRY MIXES
2.3.1 Initial Bentonite Slurry Mixture
2.3.2 Trench Bentonite Slurry Mixture
2.3.3 Additional Bentonite
2.3.4 Additives
2.3.5 S-B Backfill
PART 3 EXECUTION
3.1 General
3.2 WORKING SURFACE
3.3 SLURRY TRENCH EXCAVATION
3.3.1 Confining Stratum Excavation
3.3.2 Blasting Plan
3.4 SLURRY PLACEMENT AND TESTING
3.4.1 Slurry Placement
3.4.2 Slurry Testing
3.5 EXCAVATED MATERIAL
3.6 STABILITY
3.7 TRENCH CLEANING
3.8 S-B BACKFILL MIXING AND PLACEMENT
3.8.1 Mixing
3.8.2 Placement
3.8.3 Mixing and Placing During Cold Weather
3.8.4 Testing
3.9 SOUNDINGS
3.9.1 Elevation of Top of Confining Stratum
3.9.2 Elevation of Trench Bottom Prior to Backfilling
3.9.3 Profile of S-B Backfill Slope and Trench Bottom
3.10 AS-BUILT PROFILE
3.11 TREATMENT OF TOP OF SLURRY TRENCH
3.12 CLEAN-UP
SECTION 02 35 27
SOIL-BENTONITE (S-B) SLURRY TRENCH
NOTE: This guide specification covers the requirements for
constructing a soil-bentonite
slurry trench at both conventional and hazardous waste projects.
Comments and suggestions on this guide specification are welcome and should
be directed to the technical proponent of the specification. A listing of
technical
proponents, including their organization designation and telephone number, is
on the Internet.
Recommended changes to a UFGS should be submitted as a
Criteria Change Request
(CCR).
Use of electronic communication is encouraged.
Brackets are used in the text to indicate designer choices or locations where
text must be supplied by the designer.
PART 1 GENERAL
NOTE: In using this guide specification, the designer should realize that the
requirements for the bentonite, backfill, and construction procedure are highly
dependent on the intended purpose of the slurry trench and the environment in
which it is to be used.
The primary considerations for S-B slurry trenches are blowout requirements,
permeability, strength, and compressibility.
The S-B backfill should be designed to prevent possible blowout or piping of
the S-B backfill into the surrounding foundation material due to the hydraulic
gradient acting across the slurry trench. Design criteria are presented in
Chapter 9, Corps of Engineers (COE) EM 1110-2-1901.
The permeability for S-B slurry trenches is usually in the order of 10-6 to
10-8 cm/sec. The actual permeability of the slurry trench is dependent on both
the filter cake, which forms on the sides of the trench and the S-B backfill.
The contributions of both are dependent on the relative permeability and thickness
of the two materials. For design purposes, however, it is recommended that
the permeability of the slurry trench be based only on the S-B backfill. For
permanent or critical temporary projects, laboratory permeability tests should
be utilized in establishing the mix design.
When design requirements dictate, both shear strength and compressibility of
the S-B backfill should be analyzed by conducting laboratory testing.
Since chemical contaminants commonly associated with hazardous waste sites may
increase the permeability of S-B backfill, a compatibility testing program must
be undertaken prior to constructing a slurry trench. If the trench is to be
excavated through contaminated material, consider performing compatibility testing
using two potential backfill materials; soils to be excavated from the trench
and an uncontaminated borrow source. It should be noted that compatibility
testing can take from 2 to 6 months to complete. For this reason, it is generally
recommended that compatibility testing be completed during the design phase
of the project.
A recommended compatibility testing program consists of:
1. Free swell (ASTM D 5890) and filter cake permeability tests of several bentonites
using contaminated site ground water and site mixing water that will be used
during construction to determine acceptable bentonites for use on the project.
2. Mix design optimization tests to determine the most economical mix of soils,
dry bentonite, and bentonite slurry to produce the required permeability. This
consists of short-duration (48-72 hours) permeability tests varying the amount
of dry bentonite added (0, 2, and 4 percent) and if necessary the amount of
additional fines added (0, 10, 20 percent) using site mixing water as the permeant.
3. Long-term flexible wall permeameter testing of at least 3 S-B backfill samples:
the optimum mix design with site mixing water only as the permeant (control);
the optimum mix design with contaminated site ground water as the permeant (after
1 pore volume of site mixing water permeant to ensure a good test setup); and
a bentonite content 2 percent greater than the optimum determined in step 2
with contaminated site ground water as the permeant (after 1 pore volume of
site mixing water permeant). It is recommended that 3 pore volumes of ground
water permeant pass through the S-B backfill samples. This typically takes
at least 2 months.
To approximate field conditions in the lab, it is important to obtain contaminated
ground water and mixing water from the site. The site mixing water used during
compatibility testing shall be the water used to make the bentonite slurry during
construction.
For laboratory testing, consider requiring a permeability of one-half an order
of magnitude less than the required field permeability (for example, 5x10-8
cm/sec in the lab for 1x10-7 cm/sec in the field).
1.1 REFERENCES
NOTE: This paragraph is used to list the publications cited in the text of
the guide specification. The publications are referred to in the text by basic
designation only and listed in this paragraph by organization, designation,
date, and title.
Use the Reference Wizard's Check Reference feature when you add a RID outside
of the Section's Reference Article to automatically place the reference in the
Reference Article. Also use the Reference Wizard's Check Reference feature
to update the issue dates.
References not used in the text will automatically be deleted from this section
of the project specification when you choose to reconcile references in the
publish print process.
The publications listed below form a part of this specification to the extent referenced. The publications are
referred to within the text by the basic designation only.
| AMERICAN PETROLEUM INSTITUTE (API) |
| |
| API RP 13B-1 | | (2003) Standard Procedure for Field Testing
Water-Based Drilling Fluids |
| |
| API Spec 13A | | (1993; A 1999) Drilling-Fluid Materials |
| ASTM INTERNATIONAL (ASTM) |
| |
| ASTM C 143/C 143M | | (2005) Slump of Hydraulic Cement Concrete |
| |
| ASTM D 1140 | | (2000) Amount of Material in Soils Finer than
the No. 200 (75-micrometer) Sieve |
| |
| ASTM D 2216 | | (2005) Laboratory Determination of Water (Moisture)
Content of Soil and Rock by Mass |
| |
| ASTM D 2434 | | (1968; R 2000) Permeability of Granular Soils
(Constant Head) |
| |
| ASTM D 422 | | (1963; R 2002) Particle-Size Analysis of Soils |
| |
| ASTM D 4318 | | (2000) Liquid Limit, Plastic Limit, and Plasticity
Index of Soils |
| |
| ASTM D 5084 | | (2003) Measurement of Hydraulic Conductivity
of Saturated Porous Materials Using a Flexible
Wall Permeameter |
| |
| ASTM D 698 | | (2000ae1) Laboratory Compaction Characteristics
of Soil Using Standard Effort (12,400 ft-lbf/cu.
ft. (600 kN-m/cu. m.)) |
| U.S. ENVIRONMENTAL PROTECTION AGENCY (EPA) |
| |
| EPA 600/4-79/020 | | (1983) Methods for Chemical Analysis of Water
and Wastes |
1.2 MEASUREMENT AND PAYMENT
NOTE: Delete this paragraph when work is covered by lump-sum contract price.
1.2.1 Measurement
Measurement for S-B Slurry Trench shall be based on the area in square meters feet of completed slurry trench
measured in a vertical plane through the centerline of the slurry trench, from the top of the working surface
to the bottom of the excavated trench, and vertical lines at each corner of the full depth of the excavated trench.
Measurement shall be based on surveys and soundings taken at the site as directed and approved.
1.2.2 Payment
Payment for S-B Slurry Trench will be made at the contract unit price per square meter foot. Such price will
include costs incurred for the construction and completion of the slurry trench. No separate payment will be
made for material, equipment, handling and cleaning the slurry, quality control testing, record keeping, and
site preparation including construction of the working surface.
1.3 DEFINITIONS
NOTE: Remove items not required in the project.
The terms used in this Section are defined as follows:
1.3.1 Slurry Trench
The slurry trench is a [_____] [900] mm [3] foot minimum width trench excavated through the existing ground or
prepared working surface using the slurry method of excavation and backfilled with S-B backfill material, to
form a low permeability cutoff wall.
1.3.2 Slurry Method of Excavation
The slurry method of excavation consists of excavating a vertical walled trench and at the same time keeping
the trench filled with a bentonite slurry mixture. The purpose of the slurry is to support the walls of the
trench and prevent movement of ground water.
1.3.3 Bentonite
Bentonite is an ultrafine natural clay whose principal mineral constituent is sodium cation montmorillonite.
1.3.4 Slurry
Slurry is a colloidal mixture of bentonite and water.
1.3.5 Soil Bentonite (S-B) Backfill
S-B backfill is a homogeneous mixture of material produced by mixing soil with bentonite slurry [and additional
dry bentonite], which is placed into the excavated trench to complete the soil-bentonite slurry trench.
1.3.6 Ground Water Level
The ground water level is the piezometric level of the ground water as determined from piezometers and wells.
1.3.7 Working Surface
The working surface is the top of the [stripped and/or prepared natural ground] [or] [the surface of previously
compacted fill] from which the slurry trench shall be constructed.
1.3.8 Confining Stratum
The confining stratum is the soil stratum or rock unit to or into which the bottom of the slurry trench is excavated.
1.4 PERFORMANCE REQUIREMENTS
The Government may perform quality assurance testing on representative samples obtained by the [Contractor] [Government]
of the bentonite slurry and S-B backfill using the laboratory and equipment furnished by the Contractor. The
Government testing will in no way relieve the Contractor of the responsibility of performing tests necessary
to meet the Construction Quality Control (CQC) requirements. The Contractor shall provide the equipment and
laboratory space to government personnel on demand and these services shall be considered a subsidiary obligation
of the soil bentonite slurry trench construction. All routine testing procedures being conducted by the Contractor
shall be available for inspection by the Contracting Officer at any time.
1.5 SUBMITTALS
NOTE: Review submittal description (SD) definitions in Section 01 33 00 SUBMITTAL
PROCEDURES and edit the following list to reflect only the submittals required
for the project. Submittals should be kept to the minimum required for adequate
quality control.
A “G” following a submittal item indicates that the submittal requires Government
approval. Some submittals are already marked with a “G”. Only delete an existing
“G” if the submittal item is not complex and can be reviewed through the Contractor’s
Quality Control system. Only add a “G” if the submittal is sufficiently important
or complex in context of the project.
For submittals requiring Government approval on Army projects, a code of up
to three characters within the submittal tags may be used following the "G"
designation to indicate the approving authority. Codes for Army projects using
the Resident Management System (RMS) are: "AE" for Architect-Engineer; "DO"
for District Office (Engineering Division or other organization in the District
Office); "AO" for Area Office; "RO" for Resident Office; and "PO" for Project
Office. Codes following the "G" typically are not used for Navy, Air Force,
and NASA projects.
Choose the first bracketed item for Navy, Air Force and NASA projects, or choose
the second bracketed item for Army projects.
Government approval is required for submittals with a "G" designation; submittals not having a "G" designation
are for [Contractor Quality Control approval.][information only. When used, a designation following the "G"
designation identifies the office that will review the submittal for the Government.] The following shall be
submitted in accordance with Section
01 33 00
01 33 00
01 33 00 SUBMITTAL PROCEDURES:
SD-01 Preconstruction Submittals
Preconstruction Testing Plan[; G][; G, [_____]]
Plan providing a list of test equipment, procedures, and materials to be used to [verify]
[develop] the mix design for the S-B backfill.
Slurry Trench Implementation Plan[; G][; G, [_____]]
Plan describing the general work sequence and layout of operations. The layout of operations
shall include scale drawings, which depict slurry and S-B backfill preparation and storage areas.
The plan shall describe Contractor qualifications, equipment, method of trench excavation, [blasting,]
use or disposal of excavated material, bottom cleaning, slurry preparation and maintenance,
S-B backfill preparation and placement, and site clean-up. The plan shall provide a description
of quality control equipment and test procedures, sample test forms for reporting test results,
and the offsite laboratory proposed for use.
The Contractor shall submit data on the equipment to be used in the construction of the slurry
trench; equipment to be used to obtain [bedrock] [impervious stratum] samples; [equipment to
be used to obtain record control samples of the completed slurry trench;] and equipment to be
used in the Contractors quality control testing.
Blasting Plan[; G][; G, [_____]]
Blasting Plan, as specified, for approval.
SD-02 Shop Drawings
As-Built Profile
A scale drawing providing a log of the subsurface materials excavated from the trench, and
a profile of the completed slurry trench. [The limits of each batch of S-B backfill shall be
delineated as placed.]
SD-04 Samples
Bentonite[; G][; G, [_____]]
A minimum of 4.5 kg 10 pounds of the proposed bentonite at least [1] [_____] month prior to
use.
Backfill Material[; G][; G, [_____]]
A minimum of 22.5 kg 50 pounds of each type of proposed borrow soil at least [1] [_____] month
prior to use.
SD-06 Test Reports
S-B Backfill Test Report
A report summarizing the procedures and results of the Pre-construction S-B backfill mix tests.
The report shall include a description of mix proportions, gradations, slumps, densities, permeabilities,
and moisture contents of [_____] 3 samples of the final S-B backfill mix using the bentonite
and backfill materials proposed for use.
Quality Control Testing
The results from quality control testing.
Soundings
A record of soundings and measurements taken during construction of the slurry trench.
Water
A record of the water source and associated chemical analysis.
Bentonite Slurry Mixes
Slurry Properties
A record of bentonite slurry mix quantities, proportions of additives utilized, and adjustments
for each batch.
SD-07 Certificates
Bentonite
A copy of the test results from the bentonite manufacturer for each lot shipped to the site
and a certificate of compliance stating that the bentonite complies with applicable standards.
1.6 QUALIFICATIONS
NOTE: Remove subparagraphs not required in the project.
1.6.1 Contractor
The Contractor shall have sucessfully installed a minimum area of [_____] 100,000 square meters 1,000,000 square
feet. The qualifications and experience of personnel who shall be responsible for conducting the operations
shall include references (name and telephone number) of the owners of the Contractor's previous slurry trench
construction projects.
1.6.2 Slurry Trench Specialist
The slurry trench specialist shall be an individual who has had experience with at least [_____] [5] projects
in all aspects of slurry trench construction which includes, but is not limited to:
a. The use, testing, and control of bentonite slurries,
b. The mixing methods required to properly mix the slurry and backfill materials as required,
c. Trench excavation and backfilling procedures, and
d. A thorough knowledge of construction equipment and material testing required for slurry trench construction.
1.6.3 Slurry Trench Excavation Equipment Operator
The slurry trench excavation equipment operator shall have experience using similar slurry trench excavation
equipment to be used for this contract in a minimum of [_____] [2] projects of similar or greater magnitude (depth).
1.7 DELIVERY, STORAGE, AND HANDLING
Materials delivered and placed in storage shall be protected from the weather, dirt, dust or other contaminants.
1.8 GEOTECHNICAL SITE CONDITIONS
1.8.1 Exploratory Borings
NOTE: In most cases, the exploratory borings along the alignment should be
obtained during design. However, in some cases, it may be necessary to have
the Contractor obtain exploratory borings to determine or verify the depth or
characteristics of the key stratum. This should be performed well in advance
of slurry trench installation to prevent delays. If additional drilling is
required, it is recommended that a separate specification be prepared for that
work.
Subsurface exploratory borings have been obtained by the Government to determine the character of materials to
be excavated. Locations of the borings are shown on the drawings and the logs of those borings, which fall within
the area of this contract, are included in [_____] for the convenience of the Contractor. The Government assumes
no responsibility for interpretation or deductions made by the Contractor from the logs and borings. Local minor
variations may exist in the subsurface materials between boring locations and, if encountered, will not be considered
as being materially different within the purview of this contract [_____]. Soils classifications shown on the
logs are the result of [field visual classifications] [laboratory classifications] in accordance with the Unified
Soil Classifications System. [The results of all laboratory testing, including rock and soil, are available
for review by the Contractor in the [_____].] [Attention is invited to paragraph SUBSURFACE INVESTIGATIONS in
the Special Clauses for availability of core borings and soil samples for inspection.]
1.8.2 Subsurface Conditions
NOTE: A general description of the conditions to be encountered during the
excavation should be provided. Also, provide a description of the stratum or
formation into which the slurry trench will be keyed.
[_____].
1.8.3 Ground Water
NOTE: Provide a discussion of the ground water that could affect the slurry
trench construction.
[_____].
1.8.4 [Embankment Conditions]
NOTE: When a slurry trench is installed through an existing embankment, a description
of the embankment materials to be excavated should be provided.
[_____].
1.9 QUALITY CONTROL TESTING
The Contractor shall provide Quality Control Inspectors as necessary for bentonite slurry preparation and maintenance,
trench excavation, and S-B backfill preparation and placement.
1.9.1 Bentonite Tests
A minimum of 1 test for each specified requirement shall be performed for each truck or rail car shipment delivered
to the site.
1.9.2 Water Tests
NOTE: Acceptable slurries can generally be made from most water sources; however,
any suspect water should be tested during pre-construction tests. Water with
high hardness
A minimum of [_____] [1] test[s] for each specified requirement shall be performed for each water source used.
Testing shall be performed as specified in Table 1.
1.9.3 Backfill Material Tests
One set of backfill material tests, as specified in Table 1, shall be performed for every [_____] 500 cubic meters
yards used.
1.9.4 Slurry Properties
NOTE: It is generally recommended that after high shear mixing, the slurry
be allowed to hydrate for 8 hours before use in the trench. This process assures
that the bentonite is fully hydrated and is uniform throughout. Shorter hydration
times may be allowed if it can be shown that the prepared slurry meets or exceeds
project requirements.
[Slurry shall be required to hydrate a minimum of [8] [_____] hours prior to use.] The initial bentonite slurry
shall be tested prior to placing in the trench and a minimum of 2 times each [_____] [8] hour shift per mixing
plant.
1.9.5 S-B Backfill Tests
NOTE: The confining pressure used to perform permeability testing should be
representative of site conditions. To simulate site conditions, the confining
pressure specified should be representative of the upper quarter to one-half
of the wall depth.
Shelby tube, split spoon, or other sampling devices may be pushed into the completed
slurry trench to obtain samples for quality control testing; however, it can
be difficult to obtain quality samples of many S-B backfills, especially if
there are coarse materials in the S-B backfill. As a result, samples of S-B
backfill obtained just prior to placement in the trench are used for QA/QC,
and samples of the S-B backfill from the completed wall, if taken, may be used
for QA or for information only. The designer should determine what samples
are necessary to meet project requirements. It should be noted that permeablity
tests may take several days before results are known.
Sampling and testing shall be performed, in accordance with the approved Preconstruction Testing Plan, just prior
to placing S-B backfill in the trench as shown in Table 1. [The density of the S-B backfill shall be calculated
using a 101.6 mm 4 inch cylindrical mold as described in Paragraph 6 of ASTM D 698. S-B backfill shall be placed
in the mold and rodded 10 times. Additional S-B backfill shall then be added to fill the mold. The weight and
volume of the molded S-B backfill shall then be used to determine the density.] [The density of the S-B backfill
shall be determined using a mud balance.] Density shall be determined at a rate of 1 test for every [_____]
[1000] cubic meters yards. A sample of S-B backfill for permeability testing shall be taken just prior to placement
in the trench for every [1000] [_____] cubic meters yards. The Contractor shall submit an S-B Backfill Test
Report containing the results of the tests performed.
[1.9.6 Samples of Confining Stratum
NOTE: This paragraph is to be used if the slurry trench is to be keyed into
a confining stratum. Samples of the confining stratum can be based on examination
of samples taken from bucket cuttings or drive tube samplers. In many cases,
examination of bucket cuttings alone will be sufficient to determine when the
confining stratum has been reached. If required, samples can be obtained with
drive tube samples. Drive tubes can be pushed with the excavator bucket or
a drill rig. Remove this paragraph if not needed in the project.
Samples of the confining stratum shall be taken at [_____] meter foot horizontal intervals and at additional
intervals or depths as directed. Samples shall be obtained from [either] [excavator bucket cuttings] [drive
tube samples]. [The sampler shall be a [_____] mm inch I.D., or larger, [drive tube sampler] with a minimum
length of [_____] m feet. Samples shall be obtained by advancing the sampler a minimum of [_____] mm inches
into the confining stratum. The samples shall have a minimum length [recover] of [_____] mm inches.] After
examining these samples, the Contracting Officer will either approve the termination of excavation at the sample
points or require additional excavation. If additional excavation is required, then additional samples shall
be furnished by the Contractor as specified above. All samples shall be properly identified and labeled, placed
in sealed plastic containers and stored in a location designated by the Contracting Officer.
]PART 2 PRODUCTS
2.1 MATERIALS
2.1.1 Bentonite
NOTE: Bentonites for use may conform to either Section 4 or Section 5 of API
Spec 13A, provided the desired permeability is obtained during pre-construction
mix design and compatibility testing. Bentonites, which conform to Section
4 of API Spec. 13A, have typically been treated with small amounts of polymers.
Bentonites, which conform to Section 5 of API Spec 13A, have not been chemically
treated. For this specification, the values shown in Table 1 for bentonite,
reflect the requirements of API Spec 13A, Section 5. Values in Table 1 should
be modified accordingly for Section 4 bentonites.
In the event no bentonites conforming to either Section 4 or 5 of API Spec 13A
can produce the desired permeability due to contaminants in ground water, bentonites
or other materials with substantial chemical alterations or additives may be
used. Use of these materials will depend upon the successful completion of
a compatibility testing program and the concurrence of all appropriate State
and Federal regulatory agencies. These materials should be used with caution
due to the general lack of long-term performance data. These materials may
be proprietary products. Modify appropriate sections of this guide specification
according to manufacturer's recommendations.
The bentonite shall be sodium cation base montmorillonite powder that conforms to API Spec 13A, Section [4][5],
and Table 1, located at the end of this section. [Chemically treated bentonite will not be allowed.] [Other
chemically treated bentonites may be considered provided the required permeability values can not be obtained
with bentonites conforming with Section 4 or Section 5 of API Spec 13A.] No bentonite from the bentonite manufacturer
shall be used prior to acceptance by the Contracting Officer. Bentonite not meeting specifications shall be
promptly removed from the site at the Contractors expense. Bentonite shall be protected from moisture during
transit and storage.
2.1.2 Water
The [Contractor shall] [Government will] supply [and condition] water required for mixing with bentonite to produce
slurry. The water shall be clean, fresh, and comply with the standards specified in Table 1. The Contractor
shall furnish water quality test results for water used for mixing the bentonite slurry to assure conformance
to these standards.
2.1.3 Backfill Material
NOTE: For backfill materials with a low percentage of fines (less than 20 percent),
it may be necessary to add supplemental fines from an additional borrow area
to achieve the desired permeability.
If offsite borrow material is selected for use as the backfill material, it
should be tested to assure that it is uncontaminated. Testing requirements
should be addressed in Section 01 35 45.00 10 CHEMICAL DATA QUALITY CONTROL.
It may be possible to use material excavated from the trench as backfill material,
even if it is slightly contaminated. If contaminated material is being considered
for use, it must be verified that the material can be safely handled in the
field.
The gradation requirements below should be modified to fit the chosen backfill
material. In general, no particles greater than 76 mm (3 inches) should be
in the mix, and a minimum fines content of 20 percent is always recommended.
The backfill material shall be obtained from [material excavated from the slurry trench] [a Government furnished
borrow area] [an offsite borrow area]. Thirty days prior to utilization of any off-site borrow, the site shall
be identified and representative samples of each type of material shall be submitted to the Contracting Officer
for QA testing. Backfill shall be free of [contamination] [_____], roots, debris, brush, sod, organic or frozen
material. [Material passing the 75 micrometer No. 200 sieve shall have a liquid limit greater than [30] [_____]
and a plasticity index greater than [10] [_____]]. Materials shall be thoroughly blended prior to mixing with
bentonite slurry and shall conform to the following gradation requirements:
Screen Size or Number Percent Passing
(U.S. Standard) by Dry Weight
_________________ _____________
75 mm [_____] [100] [_____]
4.76 mm [_____] [40-80] [_____]
0.42 mm [_____] [25-60] [_____]
75 micrometer [_____] [20-40] [_____]
3 inch [_____] [100] [_____]
No. 4 [_____] [40-80] [_____]
No. 40 [_____] [25-60] [_____]
No. 200 [_____] [20-40] [_____]
2.2 EQUIPMENT
The Contractor shall furnish all necessary plant and equipment for use on this project.
2.2.1 Trench Excavation Equipment
Equipment for excavating the slurry trench shall be any type or combination of excavating equipment capable of
performing the work as specified and shown on the drawings. [The equipment shall be capable of excavating the
required minimum width of trench in a single pass of the excavating equipment.] The buckets utilized with such
equipment may be perforated, tapered and equipped with bottom-side cutter teeth protruding no more than 150 mm
6 inches. The bucket shall be designed to maintain the width of the trench and to minimize ravelling of the
trench sides during use. The equipment shall be able to reach at least [_____] 1500 mm 5 feet deeper than the
maximum depth shown on the drawings.
2.2.2 Slurry Mixing and Cleaning Equipment
The slurry mixing plant shall be equipped with a high-speed/high-shear, colloidal mixer or a high-velocity/high
pressure venturi jet mixer used in conjunction with a high-speed/high-shear centrifugal pump. The plant shall
be equipped with a mechanically or hydraulically agitated sump and shall include pumps, valves, hoses, supply
lines, tools, and other equipment and materials required to prepare the slurry and deliver it in a continuous
supply from the hydration pond [or tanks] to the slurry trench. Mixers shall be capable of achieving complete
dispersion of bentonite and additives, and shall be capable of continually mixing the slurry to provide and maintain
a uniform blended slurry. The Contractor shall have sufficient ponds [or tanks] for storage of hydrated bentonite
slurry. [Slurry cleaning equipment shall be available to reduce sand, sediment, or other solids as necessary
to maintain the sand content or density requirements of the slurry in the trench. Slurry cleaning equipment
may include but not be limited to vibratory shaker screens, centrifugal sand separators, or stilling ponds.]
2.2.3 Field Laboratory Equipment
The field laboratory shall contain as a minimum the following equipment:
a. 1 Mold and rod for slump test.
b. 2 Marsh funnel sets.
c. 1 Standard filter press.
d. 2 Mud balances (direct reading of density).
e. 1 Slurry sampler.
f. 2 Number 200 sieves.
g. 1 Set of standard sieves and sieve shaker.
h. 1 Oven for moisture content.
i. 1 Balance.
j. 1 pH [meter] [paper].
k. 2 Sand content sets.
l. 1 101.6 mm 4 inch Cylindrical mold.
2.3 BENTONITE SLURRY MIXES
2.3.1 Initial Bentonite Slurry Mixture
NOTE: For most bentonites, 4 to 6 percent by weight should produce a slurry
that will meet all the specified requirements. Other mixtures may be determined
to be acceptable during pre-construction tests. S-B backfill mix designs should
be determined during pre-construction testing. Results from the tests should
be used in Table 1.
The initial bentonite slurry mixture shall conform to the standards specified in Table 1.
2.3.2 Trench Bentonite Slurry Mixture
The trench bentonite slurry mixture shall conform to the standards specified in Table 1.
2.3.3 Additional Bentonite
If directed by the Contracting Officer, the Contractor shall thicken the slurry to a more viscous condition than
the limits specified above. The Contractor shall use additional bentonite, as directed.
2.3.4 Additives
Peptizing agents and bulking agents shall not be mixed with the slurry. Approved thinners or dispersants and
flocculants of the types used in the control of oil field drilling muds, may be used to control standard properties
of the slurry such as apparent viscosity, pH and filtration characteristics.
2.3.5 S-B Backfill
The S-B backfill, consisting of [backfill material and bentonite slurry] [backfill material, bentonite slurry,
and a minimum of [2] [_____] percent dry bentonite] shall be thoroughly mixed and shall conform to the standards
specified in Table 1 just prior to placement in the trench.
PART 3 EXECUTION
3.1 General
The slurry trench shall be constructed to the elevations, lines, grades, and cross-sections shown and in accordance
with these specifications, unless otherwise directed. The Government may modify the dimensions and quantities
of the work as determined necessary. The Contractor shall submit a Slurry Trench Implementation Plan for approval,
a minimum of [_____] weeks prior to the start of construction.
3.2 WORKING SURFACE
NOTE: The maximum slurry trench surface slope along the slurry trench alignment
during construction should be 1 percent. For sites with grades greater than
1 percent, the working surface should be designed to achieve the 1 percent slope.
If contaminated, it is common practice to remove the top 300 mm (12 inches)
of the working surface after completion of the slurry trench. Most excavation
equipment requires 6 meters (20 feet) of clearance to swing around; therefore,
a minimum working surface width of 12 meters (40 feet) is recommended. Some
equipment may require wider work platforms in order to negotiate trench corners.
At sites where S-B backfill will be mixed beside the trench, instead of at a
central mixing area, a wider working surface may be required. The slurry trench
alignment is not required to be in the centerline of the working surface.
Slurry trench construction shall be accomplished from the working surface, as shown on the drawings. If the
Contractor's operations require a wider working surface, the reason for the change shall be submitted. If approved,
a wider working surface may be constructed at no additional cost to the Government. Working surface material
and compaction requirements are described in Section [_____]. In the event that the static ground water table
is encountered at a depth of [_____] 1 m 3.0 foot or less below the designated working surface, the Contractor
shall, at the direction of the Contracting Officer, raise the working surface to a height of [_____] [1] m [3]
feet above the measured static ground water level with approved fill material. The working surface thus constructed
shall be utilized as a basis for measurement for payment.
3.3 SLURRY TRENCH EXCAVATION
NOTE: For shallow (less than 15 meters (50 feet)) slurry walls, most excavation
equipment can round trench corners with a 30 meter (100 foot) turning radius.
For trenches deeper than 30 meters (50 feet), consult with Contractors about
the required turning radius.
The excavation shall begin from the working surface and shall provide a vertical (within 2 percent) continuous
[_____] 900 mm 3 foot minimum width trench to the required depth along the centerline of the excavation. [The
slurry trench shall key [_____] 600 mm 2 feet into the [_____] stratum.] The Contracting Officer may direct
the Contractor to modify the trench depth based on examination of bucket cuttings or drive samples. The toe
of the slope of the trench excavation shall not precede the toe of the S-B backfill slope by less than [_____]
9 meters 30 feet or more than [_____] 30 meters 100 feet. At the intersection of 2 straight line segments,
the trench excavation shall extend a minimum of [_____] 1500 mm 5 feet beyond the outside of the intersection
at all depths. If trench excavation overlaps into previously completed slurry trench, the excavation shall extend
a minimum of [_____] 3 meters 10 feet into the previously placed S-B backfill at all depths. Any removed section
of completed slurry trench shall be refilled with S-B backfill at no additional expense to the Government.
3.3.1 Confining Stratum Excavation
NOTE: If the confining stratum is a competent low permeability bedrock, a very
small penetration into the bedrock may be satisfactory. High costs may result
by requiring a 600 mm (2 foot) key into competent bedrock. Remove this paragraph
if not required in the project.
The confining stratum shall be excavated the full trench width to the depths shown [or to the depth of refusal]
[or as otherwise directed]. [Any [sandstone] [_____] lenses encountered at the minimum excavation depth shall
be removed for the full width of the trench and into the underlying confining stratum.] The confining stratum
shall then be sampled in accordance with paragraph SAMPLES OF CONFINING STRATUM. Termination of excavation will
be approved by the Contracting Officer.
3.3.2 Blasting Plan
NOTE: Blasting, if necessary, may cause unanticipated adverse effects in the
subsurface. The designer should carefully evaluate the need for blasting to
remove or loosen subsurface materials. Other methods such as chiseling or modfication
of slurry trench alignment or depths should be considered prior to implementation
of any blasting. Remove this paragraph if not required in the project.
Any blasting shall be approved. Blasting shall be conducted in accordance with an approved blasting plan. The
blasting plan shall include hole spacing and depths, loading, delay sequence, type of explosives, safety program,
and any other pertinent information that will be necessary for the Contracting Officer's evaluation. Explosive
materials [shall] [shall not] be stored on the site. [On site storage shall be at [_____].] [ A drawing showing
the top and bottom elevations of the [sandstone][_____] at each blasting drill hole shall be submitted.]
3.4 SLURRY PLACEMENT AND TESTING
NOTE: Sand content of the in-trench slurry is highly dependent upon the soils
through which the trench is excavated. In many cases, typical values for sand
content can be as high as 30% without impacting the quality of the installation.
It should be noted that higher sand contents also lead to a higher density slurry.
Adjustments should be made in Table 1 regarding slurry density and sand content
limits according to site conditions. The main concern is to assure that sand
is not dropping out of the in trench slurry to the bottom of the trench in amounts
so as to affect performance of the slurry trench.
3.4.1 Slurry Placement
Slurry shall be introduced into the trench at the time excavation begins. The level of the slurry in open trenches
shall be maintained a minimum of 900 mm 3 feet above ground water level and no more than 600 mm 2 feet below
the top of the working surface until the placement of S-B backfill is complete. [If the density or sand content
of the slurry in the trench does not conform to the standards specified in Table 1, the excess solids shall be
removed from the slurry using approved methods or the slurry shall be replaced with fresh slurry.] Slurry shall
not be diluted by surface water. Conditioning of the slurry may require recirculation through a shaker screen
or the addition of approved additives. The Contractor shall have sufficient personnel, equipment, slurry storage
areas, and prepared slurry materials shall be ready to raise the slurry level at any time in the excavated trench,
weekends and holidays included.
3.4.2 Slurry Testing
The bentonite slurry in the trench shall be sampled a minimum of 2 times each [_____] [8] hour shift (near the
beginning and end of each shift), at two depths; approximately 600 mm 2 feet below the slurry surface and approximately
600 mm 2 feet above the bottom of the trench. These samples shall be taken within 1500 mm 5 feet of the toe
of the S-B backfill slope. Additional samples shall be obtained at the request of the Contracting Officer.
3.5 EXCAVATED MATERIAL
Material excavated from the trench [shall] [shall not] be used as backfill. [Excavated material to be used as
backfill shall be stockpiled for subsequent processing in approved areas.] [Excavated trench material not used
as backfill shall be placed [in the waste disposal area] [as directed].]
3.6 STABILITY
NOTE: A stability analysis should be performed during design to determine required
minimum slurry densities or levels, and to determine if any restrictions will
be required regarding stockpile placement or other loading situations. Any
site specific restrictions should be described below.
The Contractor shall be responsible for insuring and maintaining the stability of the excavated trench at all
times for its full length and depth and shall be responsible for maintaining slurry densities and levels within
specified limits. The Contractor shall control surcharges from all excavation and backfilling equipment, waste,
berm construction, backfill stockpiles, and any other loading situations that may affect trench stability. It
is the Contractor's sole responsibility to ensure that the mixing of S-B backfill and any stockpiles do not affect
the open trench stability. In the event of failure of the trench walls prior to completion of backfilling, the
Contractor shall at his expense re-excavate the trench and remove all material displaced into the trench and
take corrective action to prevent further deterioration.
3.7 TRENCH CLEANING
NOTE: The initial cleaning of the trench bottom can be accomplished with an
excavator bucket. This method of trench cleaning will generally be sufficient
for final cleaning of most projects. It is generally recommended to limit the
distance between the excavated face and the toe of the S-B backfill, as required
in Paragraph SLURRY TRENCH EXCAVATION, in order to assure trench stability.
In some cases, the air-lift pump method may be the only way to clean certain
reaches of the trench. However, the air-lift pump method can slow production,
is somewhat difficult to manuver in the trench, and may not clean the trench
bottom effectively in many cases.
Cleaning of the S-B backfill face can be difficult since the materials are very
soft and may require the excavator to track over portions of the trench that
are not yet backfilled. This procedure should only be specified when required
to meet project needs.
At a minimum, unless otherwise approved, the trench bottom shall be cleaned at the start of each [_____] [day].
[If S-B backfill placement operations have ceased for longer than [24] [_____] hours, the face of the S-B backfill
slope shall be cleaned prior to the placement of additional S-B backfill.] The trench bottom shall be probed
for any deposits or sloughed materials prior to cleaning. The trench bottom shall be cleaned by using an [excavator
bucket,] [air lift pump] or other approved equipment to ensure removal of sand, gravel, sediment, and other material
left in the trench during excavation or which has settled out of the slurry. Cleaning equipment shall not remove
material from the walls of the trench. The Contracting Officer may require more frequent cleaning. [After the
trench bottom has been cleaned, the Contractor shall sample the trench bottom with a [drive tube] [split tube]
[_____] sampler approved by the Contracting Officer. Rock surfaces that cannot be penetrated by a [drive tube]
[split spoon] sampler shall not be required to be sampled. After examining the samples, the Contracting Officer
will either approve the excavation at the points checked or require additional cleaning. If additional cleaning
is required, then additional samples shall be furnished by the Contractor as specified above.]
3.8 S-B BACKFILL MIXING AND PLACEMENT
3.8.1 Mixing
NOTE: It may be preferable to mix the S-B backfill in a separate mixing area
rather than along the side of the trench, particularly in contaminated areas,
or where off-site borrow is used for backfill materials. Other mixing methods
may include the utilization of a batch plant or pugmill operation to blend materials.
Although more expensive, these procedures may minimize operations in a contaminated
area.
The S-B backfill shall be thoroughly mixed via disking, harrowing, bulldozing, blading, or other approved methods
into a homogeneous mass, free from large lumps or clods of soil or pockets of fines, sand, or gravel. Occasional
lumps of up to [_____] [75] mm [3] inches in their largest dimension will be permitted. All particles shall
be coated with slurry. The S-B backfill may be sluiced with slurry during the mixing operations. Sluicing with
water is not permitted. The S-B backfill shall be mixed [in a separate mixing location as shown on the drawings]
[along the side of the trench]. [When mixing the S-B backfill along the side of the trench, heavy equipment
such as bulldozers shall not operate in a back and forth fashion, paralleling the open trench, closer than 5
meters 15 feet from the lip of the trench. Excess slurry may be allowed to flow back into the trench].
3.8.2 Placement
Initial S-B backfill placement shall be by one of the following methods: (1) Placement by lowering S-B slurry
to the bottom of the trench with crane and clamshell bucket, or tremie methods until the surface of the S-B backfill
rises above the surface of the slurry trench at the end of the trench; (2) Construct a lead-in trench [1H:1V]
[_____] or flatter at a point outside of the limits of work to allow a S-B backfill face to form prior to reaching
the full depth of the required slurry trench. No payments will be made for the portions of trenches which lie
outside of the limits of work. Placement operations shall proceed in such a manner that the slope of the initially
placed S-B backfill is maintained. Free dropping of S-B backfill through the slurry is not permitted. The S-B
backfill shall be placed so that it will slide down the forward face of the S-B backfill slope. The S-B backfill
shall be placed in the excavated trench so that no pockets of slurry are trapped and that a constant slope is
maintained. Placement shall be continuous from the beginning of the trench in the direction of the excavation
to the end of the trench.
3.8.3 Mixing and Placing During Cold Weather
No mixing or placing of the S-B backfill shall be performed when the air temperature is below -7 degrees C 20
degrees F. Frozen S-B backfill shall not be placed in the trench and backfill material containing frozen lumps
shall not be used to mix S-B backfill.
3.8.4 Testing
When required, additional samples for permeability testing shall be taken at [_____] intervals for the [_____]
[full depth] of the completed slurry trench using 75 mm 3 inch thin wall (Shelby) tubes. [If test results do
not meet the requirements listed in Table 1, corrective action, as determined by the Contracting Officer, shall
be taken.]
3.9 SOUNDINGS
Excavation and S-B backfill soundings shall be taken every [_____] 6 meters 20 feet along the trench centerline
using a weighted tape, cable, or other approved device. Soundings shall be measured to the nearest 30 mm 0.1
ft. The soundings shall measure the following:
3.9.1 Elevation of Top of Confining Stratum
The top of the confining stratum shall be determined based on examination of samples taken as described under
paragraph SAMPLES OF CONFINING STRATUM. This elevation shall be subject to approval.
3.9.2 Elevation of Trench Bottom Prior to Backfilling
The Contractor shall determine the elevation of the trench bottom after the trench has been cleaned and approved
as described under paragraph Trench Cleaning. This sounding shall not precede the toe of the S-B backfill slope
more than [____] 15 meters 50 feet. This elevation is subject to approval by the Contracting Officer.
3.9.3 Profile of S-B Backfill Slope and Trench Bottom
The S-B backfill slope and trench bottom shall be sounded at the beginning and end of each shift, and at additional
times as directed, at intervals of [_____] meters feet.
3.10 AS-BUILT PROFILE
An as-built profile of the trench bottom and S-B backfill slopes, including descriptions of materials encountered
in the trench bottom, shall be continuously maintained. This profile shall indicate extent of excavation and
the S-B backfill profile at the end of each work day [and after each S-B backfill batch is placed in the trench
as determined from soundings]. [The S-B backfill batch numbers shall appear on the profile with the limits of
each batch of material delineated as placed.]
3.11 TREATMENT OF TOP OF SLURRY TRENCH
NOTE: For heavy equipment crossings, it is recommended the upper portion of
the S-B backfill be excavated and a clay plug be placed under the compacted
trench cover. Additional support may be necessary to support the anticipated
loads.
Prior to placement of the compacted trench cover, a temporary [non-compacted soil] [plastic sheeting] cover shall
be placed over the trench to prevent desiccation. The temporary cover material shall be placed within [2] [_____]
days after S-B backfill placement is completed over each 30 meter 100 foot reach. If any depression develops
within the completed slurry trench area, it shall be repaired by placing and compacting additional trench cover
soil. After a minimum [two] [_____] weeks, the temporary trench cover shall be removed and replaced by a final
compacted trench cover. A final compacted trench cover [_____] mm feet wide and [_____] mm ft deep shall be
placed [as specified in Section [_____]] [to a dry density of [_____] [90] percent of maximum density at optimum
moisture to plus 3 percent in accordance with ASTM D 698]. Heavy construction equipment and machinery shall
only be driven over the slurry trench at approved heavy equipment crossing points.
3.12 CLEAN-UP
Excavation spoil, unused S-B backfill, and excess slurry shall be removed following completion of S-B backfill
placement. These materials shall be disposed of [in the waste disposal area] [at the direction of the Contracting
Officer] [_____].
TABLE 1SOIL-BENTONITE SLURRY TRENCH QUALITY CONTROL TESTING
Property Requirement Test Method
________ ___________ ___________Bentonite Powder________________
a. YP/PV Ratio [____] [1.5] max. API Spec 13A
b. Plastic Viscosity > [____] [10] API Spec 13A
c. Filtrate Loss < [____] [12.5] cubic cm API Spec 13A
d. Moisture Content < [____] [10]% ASTM D 2216
Chemical Analysis of Water__________________________
a. pH 6 to 8 API RP 13B-1
b. Hardness < [____] [50] ppm API RP 13B-1
c. Total Dissolved < [____] [500] ppm EPA 600/4-79/020
Solids Method 160.1
[ d. VOCs MCL SW-846 Method 5030B/8260B]
[ e. SVOCs MCL SW-846 Method 3510C/8270C]
[ f. TPH MCL SW-846 Modified 8015]
[ g. Metals MCL SW-846 3005A/6010C]
[ h. Pesticides MCL SW-846 3510C/8081A/8141A]
[MCL = Maximum Contaminant Level]
Initial Bentonite Slurry________________________
a. Viscosity > 40 sec API RP 13B-1
b. Density > 1025 kg/cubic m API RP 13B-1
c. Filtrate Loss < 20 cubic cm API RP 13B-1
d. pH 6.5 to 10 API RP 13B-1
In-Trench Bentonite Slurry__________________________
a. Density [____]1025-1360 API RP 13B-1
kg/cubic m
and at least
240 kg/cubic m
less than
S-B backfill
density
b. Viscosity > 40 sec API RP 13B-1
c. pH 6.5 to 10 API RP 13B-1
[d. Sand Content [____]10% max. API RP 13B-1]
Backfill Material_________________
a. Grain Size Para. 2.1.3 ASTM D 422
b. Moisture content For record ASTM D 2216
c. Fines Content Para. 2.1.3 ASTM D 1140
[d. Atterberg limits Para. 2.1.3 ASTM D 4318]
S-B Backfill_____________________
a. Slump Cone 100-150 mm ASTM C 143/C 143M
b. Density For Record ASTM D 698
and Para. 2.4.52
c. Permeability < [1 x 10-7] ASTM D 2434
[_____] cm/sec ASTM D 5084
TABLE 1SOIL-BENTONITE SLURRY TRENCH QUALITY CONTROL TESTING
Property Requirement Test Method
________ ___________ ___________Bentonite Powder________________
a. YP/PV Ratio [____] [1.5] maximum API Spec 13A
b. Plastic Viscosity > [____] [10] API Spec 13A
c. Filtrate Loss < [____] [12.5] cubic cm API Spec 13A
d. Moisture Content < [____] [10]% ASTM D 2216
Chemical Analysis of Water__________________________
a. pH 6 to 8 API RP 13B-1
b. Hardness < [____] [50] ppm API RP 13B-1
c. Total Dissolved < [____] [500] ppm EPA 600/4-79/020
Solids Method 160.1
[ d. VOCs MCL SW-846 Method 5030B/8260B]
[ e. SVOCs MCL SW-846 Method 3510C/8270C]
[ f. TPH MCL SW-846 Modified 8015]
[ g. Metals MCL SW-846 3005A/6010C]
[ h. Pesticides MCL SW-846 3510C/8081A/8141A]
[MCL = Maximum Contaminant Level]
Initial Bentonite Slurry________________________
a. Viscosity > 40 sec API RP 13B-1
b. Density > 64 pcf API RP 13B-1
c. Filtrate Loss < 20 cubic cm API RP 13B-1
d. pH 6.5 to 10 API RP 13B-1
In-Trench Bentonite Slurry__________________________
a. Density [____]64-85 pcf API RP 13B-1
and at least
15 pcf
less than
S-B backfill
density
b. Viscosity > 40 sec API RP 13B-1
c. pH 6.5 to 10 API RP 13B-1
[d. Sand Content [____]10% max API RP 13B-1]
Backfill Material_________________
a. Grain Size Para. 2.1.3 ASTM D 422
b. Moisture content For record ASTM D 2216
c. Fines Content Para. 2.1.3 ASTM D 1140
[d. Atterberg limits Para. 2.1.3 ASTM D 4318]
S-B Backfill_____________________
a. Slump Cone 4-6 inches ASTM C 143/C 143M
b. Density For Record ASTM D 698
and Para. 2.4.5
c. Permeability < [1 x 10-7] ASTM D 2434
[_____] cm/sec ASTM D 5084
NOTES:
1) If more than one (1) batching plant is being used, these frequencies shall apply to each batching plant separately.
2) Permeability tests may be performed using an approved fixed wall permeameter except that for every 5 such
tests, there shall be 1 test using a flexible wall permeameter. Fixed wall test methods and procedures shall
be submitted and approved prior to use.
3) Flexible wall permeability tests shall be performed at a maximum effective confining pressure of [_____] kPa
psi and a maximum hydraulic gradient of [30] [_____].
-- End of Section --