A5 Attachment 7 Revised Section 31 56 20 Cement-Bentonite Cutoff Wall.pdf

Big Sandy Dam Reservoir Enlargement Eden Project, Wyoming Solicitation No. 140R4020R0015

Cement-Bentonite Cutoff Wall

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SECTION 31 56 20

CEMENT-BENTONITE CUTOFF WALL

PART 1 GENERAL

1.01 MEASUREMENT AND PAYMENT

A. Cement-Bentonite Cutoff Wall:

1. Measurement: Finished area on a vertical plane through cutoff wall centerline.

a. The top of the cutoff wall shall be El. 6767.0.

b. The bottom of the cutoff wall shall be established by soundings taken in the slurry trench at the site by the Contractor in accordance with the Contractor Field Quality Control article.

2. Payment: Square foot price offered in the Price Schedule.

a. Includes development of a mix design to meet performance specifications outlined in this Section, testing of mix design and reporting results to the COR in writing.

b. Adjustments will not be made for overwidth trench due to overbreak and extra width required to construct trench around curves.

B. Additional Excavation for Cement-Bentonite Cutoff Wall:

1. Measurement: Finished area on a vertical plane through cutoff wall centerline.

a. The bottom of the cutoff wall additional excavation shall be established by soundings taken in the slurry trench at the site by the Contractor in accordance with the Contractor Field Quality Control article.

2. Payment: Square foot price offered in the Price Schedule.

a. Adjustments will not be made for overwidth trench due to overbreak and extra width required to construct trench around curves.

1.02 DEFINITIONS

A. Bentonite slurry: Mixture of bentonite and water.

B. Cement-bentonite slurry: Mixture of cement, bentonite, water, and admixtures.

Produced by adding cement and admixtures to bentonite slurry.

C. Excavation refusal: Inability of the Contractor’s production equipment to excavate more than 1 foot of depth over a bottom trench length of 20 feet within a time period of 60 minutes. Production equipment is in proper and effective operating condition and excavator bucket is equipped with ripper teeth on the back of the bucket.

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1.03 REFERENCE STANDARDS

A. American Petroleum Institute (API)

1. API 13A-10 Drilling Fluid Materials

2. API RB 13B-Sch. 1 2000 Testing Drilling Fluid Materials

B. ASTM International (ASTM)

1. ASTM C150/C150M-18 Portland Cement

2. ASTM C494/C494M-17 Chemical Admixtures for Concrete

3. ASTM C989/C989M-18 Slag Cement For Use in Concrete Mortars

4. ASTM C1602/C1602M-12 Mixing Water Used in the Production of

Hydraulic Cement Concrete

5. ASTM D2166/D2166M-16 Unconfined Compressive Strength of

Cohesive Soil

6. ASTM D4380-12 Density of Bentonite Slurries

7. ASTM D5084-16a Measurement of Hydraulic Conductivity of

Saturated Porous Materials Using a Flexible Wall Permeameter

8. ASTM D6910/D6910M-09 March Funnel Viscosity of Clay Construction Slurries

1.04 SUBMITTALS

A. Submit the following in accordance with Section 01 33 00 - Submittals.

B. RSN 31 56 20-1, Qualifications:

1. Evidence of experience and competency to construct a cement-bentonite cutoff wall. Include:

a. Documentation of experience with projects of similar size and scope.

Satisfactorily performed the work and completed the construction of at least 3 cement-bentonite cutoff walls within the last 5 years. Minimum depth of 50 feet and a minimum construction length of 1,000 feet.

b. Cement-bentonite cutoff wall onsite supervisor resume:

1) Supervised the construction of at least 3 cement-bentonite cutoff walls (or soil-bentonite or soil-cement-bentonite cutoff walls).

c. Cement-bentonite cutoff wall primary equipment operator resume:

1) Experience on at least 3 previous cement-bentonite cutoff wall contracts (or soil-cement-bentonite or soil-bentonite walls).

C. RSN 31 56 20-2, Cement-Bentonite Cutoff Wall Plan:

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1. Anticipated production rates, in square feet per day.

2. Methods and frequency of monitoring trench alignment and verticality.

3. Description of proposed method of trench excavation, including equipment and sequence of constructing cutoff wall.

4. Method of stopping rapid slurry loss during trench excavation.

5. Bentonite-water mixing method, storage area size and location, and hydration period.

6. Cement-bentonite-water mixing method and delivery method.

7. Pumping equipment, capacity, and backup equipment.

8. Type of set retarders or other additives to be used and conditions under which they will be used.

9. Method of wasting the following:

a. Cement-bentonite in pump lines due to construction difficulties or slow construction.

b. Slurry removed during trench bottom cleaning.

10. Method of flushing pump lines and disposal of flushing water after use and conditions under which flushing would be done.

11. Method of sampling bottom of slurry trench.

12. Method of winter operation of slurry system, including protection of exposed slurry surfaces and prevention of freezing water in lines and pumps.

13. Haul traffic plan.

D. RSN 31 56 20-3, Material Approval Data:

1. Name and manufacturer of each cementitious material and admixture.

a. Submit manufacturer’s test data and certification of compliance with specifications.

b. The Government reserves the right to require submission of samples of cementitious materials and admixtures for testing before or during use in cement-bentonite slurry.

2. Cementitious materials certifications and test reports:

a. Manufacturer’s certifications and test reports for each lot from which shipments are drawn.

1) Certify materials were tested during production or transfer in accordance with specified reference standard.

2) Submittal of certification and test reports shall not relieve

Contractor of responsibility for furnishing materials meeting specified requirements.

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E. RSN 31 56 20-4, Calibration Certifications:

1. Calibration certifications for all equipment used for measuring and mixing bentonite and cement-bentonite slurries.

a. Indicate that equipment was calibrated no more than 1 month before starting construction of slurry wall.

F. RSN 31 56 20-5, Mix Design.

G. RSN 31 56 20-6, Laboratory Test Results.

1. Include:

a. Permeability test results (ASTM D5084).

b. Unconfined compressive strength (ASTM D2166).

c. Filtrate loss, API RP 13B, Sec 1.

1.05 PROJECT CONDITIONS

A. Equipment shall be capable of operating and performing satisfactorily in freezing conditions.

B. Reference Appendix A of mix design report for reservoir water chemistry. Refer to Section 51 00 40 – Cement-Bentonite and Cement-Slag-Bentonite Slurry Mix Design.

PART 2 PRODUCTS

2.01 MATERIALS

A. Cement:

1. ASTM C150, Type II.

2. Meet equivalent alkalies requirements of ASTM C150 - Table 2

3. Meet false-set requirements of ASTM C150 - Table 4.

B. Bentonite: Natural sodium cation-base montmorillonite, premium-grade powdered Wyoming bentonite, in accordance with API 13A – Section 10.

1. Chemically treated bentonite not allowed.

2. Sodium montmorillonite clay purity, minimum: 85 percent.

3. Moisture content as packaged, maximum: 10 percent.

C. Slag:

1. ASTM C989, Grade 100 or 120.

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D. Water: ASTM C1602, including optional requirements C and D of Table 2 (alkali and total dissolved solids).

E. Admixtures:

1. Set extenders: ASTM C494.

a. Do not use chemical admixtures that contain more than 0.1 percent chloride, by weight.

2.02 SLURRY MIX

A. Cement-bentonite slurry: Consist of ingredients within the proportion ranges shown in Table 31 56 20A - Cement-Bentonite Slurry Mix.

Table 31 56 20A - Cement-Bentonite Slurry Mix

Mix Component Percent Added by Weight

Cement 18 to 20 percent

Bentonite 4 to 6 percent

Slag(1) 50 to 80 percent

Additive As approved by COR

Set extenders As approved by COR

(1) Percent of slag replacing total cementitious material.

B. Cured cement-bentonite shall have the following properties:

1. Permeability of hardened slurry mix, ASTM D5084: Less than or equal to 10-6 centimeters per second at 28 days.

2. Unconfined compressive strength, ASTM D2166:

a. Minimum 28 days: 20 lb/in2. This requirement applies to all samples.

b. Maximum 56 days: 100 lb/in2. This requirement applies to only the samples obtained from the point of slurry discharge into the trench (‘A’ samples).

3. Filtrate loss, API PR 13B, Sch. 1: 15-20 cm3 at 100 lb/in2.

C. Develop and test a mix design including the use of additives, site water, and set extenders to the cement-bentonite slurry. The cured cement-bentonite shall have the properties indicated above.

D. Government will evaluate the mix design test results for acceptance.

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PART 3 EXECUTION

3.01 EQUIPMENT

A. Slurry equipment:

1. Mixers: High-speed colloidal-type.

a. Fitted with adequate measuring devices, such as water meters and balances, to ensure that materials are being mixed in the correct proportions.

1) Meters and balances:

a) Calibrated in 0.1-cubic foot and 0.5-pound increments, respectively.

b) Accuracy: Plus or minus 5 percent.

c) Recalibrate as directed within 7 days after receiving written notice from the COR.

2. Holding tank(s):

a. Capacity: Sufficient to allow full hydration of the bentonite.

b. Equipped with adequate equipment to agitate the bentonite slurry to maintain particles in suspension.

3. Pumping equipment:

a. Pumps: Capable of pumping slurries from mixers to holding tanks, holding tanks to mixers, and from mixers to trench excavation or location where material can be wasted.

b. Pipes and hoses:

1) Pipes and hoses: Capable of withstanding pumping pressures.

2) Provide with couplings capable of withstanding pumping pressures.

3) Repair leaking joints, or pipes, or hoses immediately following notification.

4. Auxiliary equipment:

a. Sampling facilities: Adequate for obtaining slurry samples as specified.

b. Temperature support equipment:

1) Required to maintain slurry mixes with temperature range of 40 to 90 degrees F.

2) May include water heaters and insulating materials.

5. System flushing:

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a. Demonstrate capacity to flush the cement-bentonite slurry supply lines if cement-bentonite slurry setup is likely due to construction delays, poor mixing, or other cause.

B. Excavating equipment:

1. Capable of excavating 30-inch-wide trench through compacted embankment, overburden soil and underlying weathered foundation rock. Refer to Section 53 10 00 – Geologic Investigations.

2. Capable of continuously excavating 30-inch-wide trench to the full depth shown on the drawings.

3. The Contractor shall modify or replace equipment when necessary, as determined by the COR, to maintain production rates in accordance with the Contractor’s construction schedule.

3.02 CONSTRUCTION

A. Slurry preparation:

1. Mix bentonite slurry and cement-bentonite slurry in colloidal mixer. Do not mix slurries in trench or by hand.

2. Blend bentonite and water in high-speed colloidal-type mixer to attain complete dispersion of the bentonite particles.

3. Store bentonite slurry in holding tank(s) sufficient time to allow full hydration of bentonite.

a. Full hydration of bentonite is considered accomplished when the viscosity properties of bentonite slurry stabilize.

1) Minimum Marsh Funnel viscosity, ASTM D6910: 34 seconds.

2) Minimum density: 64 lb/ft3.

b. Continuously agitate bentonite slurry in holding tank(s) until used.

1) Agitation of slurry may be discontinued overnight or during weekends when no work is performed.

2) At beginning of each workday, stored bentonite slurry shall be agitated for at least 1/2-hour, before being used for production of cement-bentonite slurry.

4. After bentonite is fully hydrated, blend bentonite slurry with cement and admixtures in high-speed colloidal type mixer.

a. Agitation in holding tank shall impart adequate energy to cement-bentonite slurry to break down the “false set” that is sometimes produced when cement is introduced into the bentonite slurry.

b. Mix cement-bentonite slurry until fill dispersion of cement particle is obtained.

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1) Full dispersion of cement particles will be determined by the COR based on visual observations.

2) Minimum Marsh Funnel viscosity, ASTM D6910: 40 seconds.

3) Minimum density: 70 lb/ft3.

c. Do not store cement-bentonite slurry more than 3 hours before use.

1) Agitate cement-bentonite slurry continuously during storage.

2) Waste cement-bentonite slurry stored more than 3 hours, at no cost to the Government.

a) Dispose of waste cement-bentonite slurry in Zone 5A and waste areas shown on drawings.

d. Store sufficient cement-bentonite slurry to compensate for slurry loss into fractured bedrock.

B. Cutoff Wall Construction:

1. Continuously excavate trench to the lines and grades shown on the drawings.

a. Alignment of the cement-bentonite cutoff wall shall be located as shown on drawings.

b. Minimum trench width: 30 inches.

c. Depth: Excavate to the depth shown on drawings, as approved by the

COR, or until refusal. Maximum depth shall be 45 feet.

d. When determined by the COR, excavate and deposit material from the bottom of the trench to allow the Government to inspect excavated material and determine type of material located at the bottom of the trench.

2. Introduce cement-bentonite slurry into the trench at start of excavation.

3. Maintain cement-bentonite slurry within 1-foot below top of trench during excavation.

a. Trench excavation process shall not proceed faster than the capacity of slurry mixing and handling equipment to keep the trench full of slurry.

4. If trench excavation is halted long enough for the cement-bentonite slurry in the working area to set up, when excavation is restarted at least 5 feet horizontally of hardened cement-bentonite slurry shall be excavated for the entire depth of the trench.The trench excavation shall extend at least 5 feet horizontally for the entire depth of the trench into a previously placed panel of hardened CB slurry at the beginning of each new shift. Excavating 5 feet into an existing panel of CB backfill shall also be required following equipment breakdowns and other delays lasting multiple hours, at the discretion of the COR.

5. Deposit excavated trench material on upstream face of dike.

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a. Immediately remove excavated trench material from the dike crest.

6. After initial slurry set, remove any free water and fill the trench to within 6 inches of the top of the dam embankment with additional cement-bentonite slurry.

a. Expected time between completing a section of trench and placing additional cement-bentonite slurry:

1) Minimum: 3 days.

2) Maximum: 7 days.

7. Avoid equipment travel over cutoff wall until cutoff wall cap is constructed.

8. After slurry has cured for at least 28 days, construct final embankment crest as shown on drawings.

a. Excavated cutoff wall shall be deposited on upstream face of dike.

b. Place embankment material in horizontal lifts and compact in accordance with Section 31 23 02 – Compacting Earth Materials.

9. After excavated material from cutoff trench has sufficiently dried out to be worked, grade excavated material from cutoff trench and excavated material from french cap in accordance with Section 31 24 20 – Placing Cement-Bentonite Wall Spoils, Zone 5A Material.

3.03 ADDITIONAL EXCAVATION

A. If unsuitable material is encountered for the excavated trench foundation as determined by the COR, perform additional excavation to remove unsuitable material.

B. Perform additional excavation beyond specified lines as approved by the COR.

C. Overlap trench excavation at least 4 feet horizontally when the trench alignment changes by 15 degrees or more between two adjacent reaches of excavation.

D. Refill additional excavation with cement-bentonite slurry.

3.04 CLEANUP

A. Clean up slurry wastes, debris, and leftover materials resulting from the cement-bentonite cutoff wall construction process in accordance with Section 01 74 00 – Cleaning and Waste Management.

B. Slurry mixing areas remaining on site should be graded to a slope no greater than 4:1 (H:V) which allows for normal surface drainage and covered with a 6-inch lift of fill material. The final cleanup of slurry mixing areas is subject to approval by the COR.

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3.05 CONTRACTOR FIELD QUALITY TESTING

A. Perform full-scale test of slurry mixing, handling, pumping, placing, and testing procedures before starting production.

1. Notify COR at least 10 days before test.

B. Contractor shall be responsible for performing measurements and testing outlined in Table 31 56 20B – Field Quality Control.

Table 31 3056 020B – Field Quality Control

Measurement, Samples, and Tests

Spatial Frequency1 Testing Frequency1

Measure trench depth by sounding in presence of the COR

Maximum spacing every 10 horizontal feet for relatively straight portions of trench and every 5 horizontal feet within 10 feet of a change in trench alignment.

At least 2 times per shift;

following cleanout after trench collapse or sloughing of sidewalls; and before and after a shutdown period lasting more than 8 hours.

Minimum slurry sampling for laboratory testing:

‘A’ samples – obtained from the discharge end of the pipe used fresh slurry into convey bottom third of trenchcement-bentonite-slag slurry to the trench ‘B’ samples – obtained from fresh slurry in bottom third of trench

Collect ‘A’ samples a minimum of every 250 linear feet of trench. Create a minimum of 3 test cylinders for every ‘A’ Sample2.

Collect ‘B’ samples a minimum of every 250 linear feet of trench. Create a minimum of 3 test cylinders for every ‘B’ Sample2.

Stagger ‘A’ and ‘B’ samples so that they are at least 50 horizontal feet apart.

Collect at least one ‘B’ sample following a period of additional trench bottom cleaning to remove slough and/or to correct an instance of trench collapse.

Permeability of hardened slurry mix using a flexible wall permeameter (ASTM D5084)

Stagger tests between ‘A’ and ‘B’ samples and perform at least 1 test for every 500 linear feet of trench.

N/A

Unconfined compressive strength

(ASTM D2166)

Stagger tests between ‘A’ and ‘B’ samples and perform at least 1 test for every 500 linear feet of trench.

Perform one test at 28 days and the other at 56 days.

Perform 56-day tests on both ‘A’ and ‘B’ Samples;

however, maximum strength requirements will only be applied to ‘A’ samples.

pH of batch water prior to mixing N/A At least once per day.

pH of slurry in trench N/A At least once per day.

March Funnel Viscosity (ASTM D6910)

Every 200 feet of trench. At least once per 8-hour shift.

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Table 31 3056 020B – Field Quality Control

Measurement, Samples, and Tests

Spatial Frequency1 Testing Frequency1

Mud Balance Density (ASTM D4380)

Every 200 feet of trench. At least once per 8-hour shift.

Note: 1. When the spatial or time requirements for testing frequency differ, the Contractor shall adhere to the requirement that results in the largest number of tests.

2. Contractor may elect to cast more sample cylinders than the three-cylinder minimum at their own discretion. See requirements in Article 3.08.C.

C. Additional Requirements:

1. Sound trench with a weighted cable or similar device approved by the COR.

a. Record sounding depths from existing ground surface, not top of slurry.

b. Do not use measuring tapes that have been damaged or shortened.

3.06 GOVERNMENT FIELD QUALITY ASSURANCE

A. The Government will perform the following tests outlined in Table 31 56 20C – Government Quality Assurance.

Table 03 30 0031 56 20C – Government Quality Assurance

Measurement, Samples, and Tests

Spatial Frequency1 Testing Frequency1

Observe trench depth by sounding performed by Contractor.

See Table 31 56 20B – Field Quality Control.

See Table 31 56 20B – Field Quality Control.

Obtain grab samples of excavated bedrock material and visually describe excavated rock.

One every 100 feet or when distinct material changes occur.

N/A

Obtain fresh slurry samples from bottom third of trench.

Collect slurry samples a minimum of every 500 linear feet of trench. Create a minimum of 3 test cylinders for every location sampled.

Stagger Government-obtained slurry samples at least 50 feet from Contractor-obtained slurry samples.

Collect at least one sample following a period of additional trench bottom cleaning to remove slough and/or correct an instance of trench collapse.

Permeability of hardened slurry mix using a flexible wall permeameter (ASTM D5084)

At least 1 test every 1,000 feet; perform first test within first 500 feet of constructed cutoff wall.

N/A

Unconfined compressive strength

(ASTM D2166)

At least 1 test every 1,000 feet; perform first test within first 500 feet of constructed cutoff wall.

Perform one test at 28 days and the other at 56 days.

pH of batch water prior to mixing N/A At least once per day.

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Table 03 30 0031 56 20C – Government Quality Assurance

Measurement, Samples, and Tests

Spatial Frequency1 Testing Frequency1 pH of slurry in trench N/A At least once per day.

March Funnel Viscosity (ASTM D6910)

Every 200 feet of trench. At least once per 8-hour shift.

Mud Balance Density (ASTM D4380)

Every 200 feet of trench. At least once per 8-hour shift.

Note: 1. When the spatial or time requirements for testing frequency differ, the Government will adhere to the requirement that results in the largest number of tests.

3.07 TRENCH INSTABILITY AND SLURRY LOSS

A. Maintain stability of the excavated trench for its full length and depth and maintain required slurry levels and densities needed to support the trench.

B. Control surcharges from excavation and backfilling equipment; temporary spoils piles and stockpiles; and other loading situations that may affect stability of the trench.

C. Maintain stability of the open trench at all times.

D. In the event that the trench walls fail or otherwise sloughs into the excavation prior to the backfill becoming firm; re-excavate and remove collapsed material and mobilized backfill that cracks or is otherwise negatively affected at the Contractor’s expense.

E. A portion of the cement-bentonite-slag slurry is anticipated to bleed into fractures in the bedrock and may require routinely adding additional slurry into the trench during production. However, notify the COR immediately if rapid and unexpected amounts of slurry loss occur in the trench.

3.08 REJECTED CUTOFF WALL SECTION

A. In the event that the specified dimensions, gradation, gradation, or permeability, and strength requirements are not achieved, and/or in the event that windows of non-C-B backfill are present in the cutoff wall, including windows of bedrock fragments and soil, the section of the cement-bentonite cutoff wall will be rejected. The limits of the rejected section will be defined by the COR. In the absence of multiple samples at different stations being available to identify the limits of the deficient section,The the deficient section willshall be no less than the limits of the day’s production from which the permeability test sample was collected.

B. If the problem is the dimension of the wall, the Contractor shall first have to demonstrate the required width of the wall is present for greater than 90 percent of the rejected length of the wall. If the required width of the wall is present, the wall section may be approved by the COR.

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C. If the problem is gradationstrength or permeability, the Contractor has the option to test 2 additional cylinders shall collect 2 additional samples from 2 locations within the rejected section of the wall for further gradationstrength and permeability testing. If the tests are within the specified requirements, the wall section may be approved by the

COR.

D. In the event that the Contractor cannot demonstrate that the wall is within the specified requirements, the rejected section of the wall shall be re-excavated and re-constructed in accordance with this Section.

END OF SECTION

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