A07.02-AMD_02-31_56_15.pdf

ARCF Natomas Reach H 2068

SECTION TABLE OF CONTENTS

DIVISION 31 - EARTHWORK

SECTION 31 56 15

SOIL BENTONITE (SB) CUTOFF WALL - VERTICAL CHAIN TRENCHING (VCT) METHOD

PART 1 GENERAL

1.1 SUMMARY

1.2 REFERENCES

1.3 GENERAL CONDITIONS

1.3.1 Lines and Grades

1.3.2 Conduct of Work

1.3.3 Access and Ramps

1.3.4 Protection of Existing Facilities

1.3.5 Permits

1.3.6 Construction Method

1.3.7 Sequencing of the Work

1.3.8 Water for Construction

1.4 DEFINITIONS

1.4.1 Cutoff Wall

1.4.2 Bentonite

1.4.3 Vertical Chain Trenching Method

1.4.4 Ground Water Level

1.4.5 Working Surface

1.4.6 Key-In Material

1.4.7 Cutoff Wall Specialist

1.4.8 Cutoff Wall Excavation Equipment Operator

1.4.9 Quality Control Laboratory

1.4.10 Quality Control Report

1.4.11 Excavation Refusal

1.4.12 Obstructions

1.4.13 Elevation Datum

1.5 SUBMITTALS

1.6 QUALIFICATIONS

1.6.1 Contractor Qualifications

1.6.2 VCT Cutoff Wall Specialist and Cutoff Wall Excavation Equipment

Operator

1.6.2.1 VCT Cutoff Wall Specialist

1.6.2.2 VCT Cutoff Wall Excavation Equipment Operator

1.6.3 Quality Control Laboratory

1.7 DELIVERY, STORAGE, AND HANDLING

1.8 GEOTECHNICAL SITE CONDITIONS

1.8.1 Exploration

1.8.2 Ground Water

1.8.3 Knowledge of Subsurface Data

PART 2 PRODUCTS

2.1 GENERAL

2.2 BENTONITE

2.3 WATER

2.3.1 Source

2.3.2 Water Quality

31 56 15 - 1

AMENDMENT

2.4 VCT SOIL-BENTONITE MIXTURE

2.5 MATERIAL STORAGE FACILITY

2.6 ENVIRONMENTAL PROTECTION

2.7 DISPOSAL SITE

2.8 TRENCH PLATES

2.9 EQUIPMENT

2.9.1 VCT Excavation Equipment

2.9.2 VCT Mixing Equipment

2.9.3 Field Laboratory Equipment

2.9.4 Hauling Equipment

2.9.5 Equipment Weight, Speed, and Width

2.10 CONSTRUCTION STAKING

2.10.1 Initial and Final Elevation

2.11 PERMANENT METAL MARKER STAKES

PART 3 EXECUTION

3.1 GENERAL

3.1.1 VCT Cutoff Wall Implementation Plan

3.2 SITE WORK

3.3 WORKING SURFACE

3.3.1 Construction Staking

3.3.2 Construction of Working Surface

3.4 VCT SB CUTOFF WALL CONSTRUCTION

3.4.1 General

3.4.2 Cutoff Wall Key-In Verification Explorations and Monitoring

3.4.3 VCT Demonstration Section

3.4.4 Monitoring

3.4.4.1 Cutter Chain Rotation Speed and Advancement Rate

3.4.4.2 Bentonite Injection Rate

3.4.4.3 Bentonite Injection Modifications

3.4.5 Vertical Tolerance

3.4.6 Bottom Depth

3.4.7 Trench Stability

3.4.8 Continuity of Cutoff Wall

3.4.9 Top of Cutoff Wall

3.4.10 Temporary Cap

3.4.11 Settlement Plate Installation and Monitoring

3.4.12 Removal of Temporary Cap and Settlement Plates

3.5 VCT CONSTRUCTION ISSUES

3.5.1 High Water Event

3.5.2 Cutoff Wall Protection

3.5.3 Cleanup

3.6 AS-BUILT PROFILE

3.7 MIXING WATER AND WASH WATER

3.7.1 Mixing Water

3.7.2 Wash Water

3.8 QUALITY CONTROL

3.8.1 General

3.8.2 Access to Work Site

3.8.3 Cutoff Wall Mix Quantities

3.8.4 Trench Sampling

3.8.5 Protocol for Custody of Samples

3.8.6 Testing

3.8.6.1 Field Testing

3.8.6.2 Laboratory Testing

3.8.6.3 Hydraulic Conductivity Testing

3.8.6.4 Coordination of Testing Laboratories

3.8.7 Quality Control Reports

31 56 15 - 2

3.8.7.1 Daily Quality Control Report

3.8.7.2 Weekly Quality Control Report

3.8.8 Quality Control Records

3.8.9 Rejected VCT Cutoff Wall Sections

3.9 QUALITY ASSURANCE TESTING

3.10 CUTOFF WALL CLOSE OUT AND ACCEPTANCE

3.10.1 Construction Records

3.10.2 Construction Documentation

3.10.3 Construction Quality Control Test Results

3.10.4 Construction Log

3.10.5 As-Built Drawing

3.10.6 Acceptance

3.10.7 Acceptance Criteria

-- End of Section Table of Contents --

31 56 15 - 3

SECTION 31 56 15

SOIL BENTONITE (SB) CUTOFF WALL - VERTICAL CHAIN TRENCHING (VCT) METHOD

PART 1 GENERAL

1.1 SUMMARY

The work covered by this section consists of furnishing all plant, labor, equipment, and materials and of performing all operations in connection with the construction of a seepage cutoff wall, in accordance with these specifications and applicable plans. The cutoff wall construction method addressed by this specification is the Vertical Chain Trenching (VCT) method. The intent of the cutoff wall is to provide permanent, continuous, homogeneous, and low permeability barrier to embankment and foundation seepage within the vertical depth limits and horizontal station limits shown on the Plans. The soil-bentonite (SB) cutoff wall shall be constructed from the working surface as identified on the plans by the VCT method from the degraded crown of the levee.

1.2 REFERENCES

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 (2009; Errata 2014) Recommended Practice for Field Testing Water-Based Drilling Fluids

API Spec 13A (2010; Errata 1 2014; Errata 2-3 2015) Specification for Drilling-Fluid Materials

ASTM INTERNATIONAL (ASTM)

ASTM C117 (2013) Standard Test Method for Materials Finer than 75-um (No. 200) Sieve in Mineral Aggregates by Washing

ASTM C136/C136M (2014) Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates

ASTM C143/C143M (2015) Standard Test Method for Slump of Hydraulic-Cement Concrete

ASTM D3740 (2012a) Minimum Requirements for Agencies Engaged in the Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction

ASTM D5084 (2010) Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter

31 56 15 - 4

ASTM D7263 (2009) Standard Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens

U.S. ENVIRONMENTAL PROTECTION AGENCY (EPA)

EPA 600/4-90/027F (1993) Methods for Measuring the Acute Toxicity of Effluents and Receiving Waters to Freshwater and Marine Organisms

STATE OF CALIFORNIA DEPARTMENT OF TRANSPORTATION (CALTRANS)

Bridge Design Manual (2004) Bridge Design Specifications

CA MUTCD (2012) California Manual on Uniform Traffic Control Devices

URS CORPORATION (URS)

REACH H GDR (2016) Geotechnical Data Report, American River Common Features Project Natomas Basin - Reach H

1.3 GENERAL CONDITIONS

1.3.1 Lines and Grades

The Contracting Officer may at any time prior to or during construction require a change in the cutoff wall depth. The objective of the cutoff wall is to block potential seepage through the levee embankment and/or through the levee foundation materials. The cutoff wall may be optimized by increasing or decreasing the depth of the cutoff wall. The potential variation from the depth indicated in the Plans is estimated to be plus or minus five feet, but Contractor's excavating equipment shall be capable of excavating a maximum of 10 feet deeper than the depth indicated on the Plans. However, between Station 44+50 and Station 50+00, the excavating equipment will not be required to excavate below the depth shown on the Plans.

1.3.2 Conduct of Work

Maintain and protect the cutoff wall in a satisfactory condition at all times until final completion and acceptance of all work under the Contract.

1.3.3 Access and Ramps

See Section 01 50 02 TEMPORARY CONSTRUCTION FACILITIES and Section 31 00 00 EARTHWORK for details and requirements for access and ramps.

1.3.4 Protection of Existing Facilities

Construction shall be conducted in a manner that avoids damage to all existing facilities that are not designated for removal or reconstruction.

1.3.5 Permits

The Contractor and subcontractors shall obtain and pay all necessary fees for all local, state, and federal permits required of the Contractor and

31 56 15 - 5 subcontractors to accomplish the Work.

1.3.6 Construction Method

The cutoff wall method shall be constructed using water and bentonite mixed in proper proportions with soil to achieve a homogenous mixture with the permeability properties required by the Specifications. Soil for the cutoff wall mix shall be mixed in-place. This specification includes requirements for the in-place mixing of soil and bentonite using a vertical chain mixing system.

1.3.7 Sequencing of the Work

The Contractor may use multiple headings to achieve the required schedule completion dates. Consult section 00 73 05 SUPPLEMENTAL CONDITION REQUIREMENTS FOR REACH H for any information regarding using multiple work shifts per day to achieve the required schedule completion dates.

1.3.8 Water for Construction

Details regarding water supplies, and the pumping and conveyance of the water, are presented in Section 01 50 02, TEMPORARY CONSTRUCTION FACILITIES. This water source will be used for all trial mixes and production.

1.4 DEFINITIONS

1.4.1 Cutoff Wall

The cutoff wall is a 30-inch-wide trench constructed from the prepared working surface using the VCT method to form a low permeability cutoff wall with a specified maximum permeability.

1.4.2 Bentonite

Bentonite is an ultrafine natural clay whose principal mineral constituent is sodium cation montmorillonite.

A copy of the test results from the bentonite powder manufacturer for each lot shipped to the site and a certificate of compliance stating that the bentonite complies with API Spec 13A.

1.4.3 Vertical Chain Trenching Method

The VCT method is accomplished via a continuous vertical chain that rotates at high speeds that is inserted into the ground. VCT equipment is equipped with: metered bentonite delivery systems and underground water injection nozzles; as applicable pre-mixed slurry injection ports; monitored speed controls for both the mixing chain and horizontal advancement; and GPS mapping and laser guides to control depth and locations. Once the VCT reaches the design depth it advances horizontally and from that point, VCT equipment shall cut a continuous trench (on a straight or curved alignment) while mixing the soil in situ with metered amounts of bentonite (dry or slurried). Because of the high-speed rotation of the cutter chain, a relatively uniform mix (soil, bentonite and water) can be prepared.

1.4.4 Ground Water Level

The ground water level is the piezometric level of the ground water as

31 56 15 - 6 shown on the exploration logs. Groundwater levels indicated on the exploration logs were levels found at the time of exploration. The groundwater table can vary significantly depending on time of year, variation from normal precipitation, and the water levels in NEMDC Channel.

1.4.5 Working Surface

The working surface is the top of the degraded levee crown, prepared as shown on the Plans and described in the Specifications, from which the cutoff wall shall be constructed.

1.4.6 Key-In Material

The key-in material is the soil stratum into which the bottom of the cutoff wall is embedded.

1.4.7 Cutoff Wall Specialist

The cutoff wall specialist is an individual working for the Contractor who will have responsibility for the construction of the VCT cutoff wall.

1.4.8 Cutoff Wall Excavation Equipment Operator

The excavation equipment operator is an individual who will operate the excavation equipment used to construct the VCT cutoff wall.

1.4.9 Quality Control Laboratory

Contractor's quality control laboratory shall perform quality control testing on material samples to verify compliance with the Specifications.

1.4.10 Quality Control Report

A report prepared by the Contractor for each shift and for each rig (if multiple headings of the cutoff wall are advanced) that documents the progress on the VCT cutoff wall construction and present the results of the quality control inspection and testing.

1.4.11 Excavation Refusal

The Contracting Officer will determine when excavation refusal is reached.

Excavation refusal will be defined as the inability of the Contractor's approved production excavator to excavate more than one foot of depth over a bottom trench length of 30 feet in a period of 60 minutes with excavator equipment in proper and effective operating condition utilizing the equipment discussed in the paragraph VCT EXCAVATION EQUIPMENT.

1.4.12 Obstructions

The Contracting Officer shall be the sole judge of whether an obstruction has been encountered. Culverts, standpipes, and other buried piping that are shown on the Plans, or marked by underground service alert (USA) and that are either to be preserved and protected or removed and replaced as part of the Work shall not be considered obstructions. Existing utilities shown on the Plans shall not be considered obstructions.

Naturally-occurring materials such as cobbles and boulders shall not be considered obstructions.

31 56 15 - 7

1.4.13 Elevation Datum

All elevations are referenced to the North American Vertical Datum of 1988 (NAVD-88) in feet.

1.5 SUBMITTALS

The following shall be submitted in accordance with Section 01 33 00

SUBMITTAL PROCEDURES.

SD-01 Preconstruction Submittals

All Preconstruction Submittals shall be submitted no later than 30 calendar days after Notice-to-Proceed.

VCT Cutoff Wall Implementation Plan; G, DO

Including the required tie-in verification exploration plan.

Demonstration Section Design and Implementation Plan; G, DO

Results of the Demonstration Section; G, DO

VCT Cutoff Wall Quality Control Program; G, DO

Contractor Qualifications; G, DO

Water Quality Test Results; G, DO

Quality Control Laboratory Qualifications; G, DO

Remediation Plan; G, DO

Demonstration Section Test Report; G, DO

SD-04 Samples

Bentonite;

SD-06 Test Reports

Daily Quality Control Report; G, DO

Weekly Quality Control Report; G, DO

Laboratory Testing Report; G, DO

SD-07 Certificates

Bentonite Powder Manufacturer Test Results; G, RO

Calibration of Scales and Flow Meters; G, RO

SD-11 Closeout Submittals

Construction Records; G, DO

Construction Documentation; G, DO

31 56 15 - 8

Construction Log; G, DO

As-built Drawing; G, DO

1.6 QUALIFICATIONS

1.6.1 Contractor Qualifications

This paragraph is reserved.The Contractor, his subcontractor, joint venture partner, or merged company shall have successfully constructed a minimum two VCT cutoff wall projects in the last 5 years of similar size and complexity as this project with similar access constraints, and similar depth and length. Consider multiple cutoff wall segments under one contract to be one project. The qualifications and experience of personnel who shall be responsible for conducting the operations shall include references of the previously completed project owners with owner name;

telephone number; address; and project description including depth, length, and construction method of the Contractor's previous successful VCT cutoff wall construction projects. An individual's experience from former companies shall not qualify as the present company's experience. However this experience can be used as individual experience such as for the slurry cutoff wall specialists. Submit Contractor Qualifications for approval.

1.6.2 VCT Cutoff Wall Specialist and Cutoff Wall Excavation Equipment Operator

Maintain an VCT cutoff wall specialist and equipment operator at the site on a full-time basis while the cutoff wall is being constructed. The primary or alternate employee shall be committed to the Contractor for the duration of the project, unless a written release is obtained from the Contracting Officer's Representative.

Provide VCT cutoff wall specialist qualifications as part of the Contractor Qualifications submittal for approval. Qualifications must meet the requirements of paragraph VCT CUTOFF WALL SPECIALIST.

Provide VCT cutoff wall excavation equipment operator qualifications as part of the Contractor Qualifications submittal for approval.

Qualifications must meet the requirements of paragraph VCT CUTOFF WALL EXCAVATION EQUIPMENT OPERATOR. If the Contractor utilizes multiple headings, submit qualifications for slurry cutoff wall excavation equipment operators for each heading.

The following information shall be submitted to the Government for both the VCT cutoff wall specialist and VCT cutoff wall excavation equipment operators:

a. Name, address, and telephone number of customer and point of contact for projects forming the experience record.

b. Contract number, contract amount, date of award, and date of completion of the project forming the experience.

c. VCT cutoff wall length and depth.

d. A copy of the portion of the specification requirement from the reference project indicating the required wall acceptance criteria (i.e., hydraulic conductivity) or a letter of reference from the owner for each project submitted that briefly describes the specification

31 56 15 - 9 requirements.

e. Description of the method of construction and excavation equipment used.

1.6.2.1 VCT Cutoff Wall Specialist

The cutoff wall specialist shall provide supervision and control of the composition, mixing, placing, and maintenance of the VCT mix. The cutoff wall specialist shall be onsite at all times during cutoff wall construction. The cutoff wall specialist experience shall include, but is not limited to:

a. Controlling composition, mixing, placing, testing, and maintaining the VCT excavation mixing process.

b. Supervision of alignment, verticality, and depth of cutoff walls.

c. The mixing methods required to properly control mixing and properly mix the cutoff well as required.

d. A thorough knowledge of VCT cutoff wall construction equipment and material testing required for cutoff wall construction.

e. Show successful construction of at least two VCT cutoff walls within the last 5 years, having similar access constraints and at a minimum as deep. Project experience not in North America may be cited, however subject to approval based on verification.

1.6.2.2 VCT Cutoff Wall Excavation Equipment Operator

Each cutoff wall excavation equipment operator shall have previously successful experience using similar cutoff wall excavation equipment to be used for this contract in a minimum of 2 successfully completed projects of similar complexity.

1.6.3 Quality Control Laboratory

The Contractor's quality control laboratory shall be an independent commercial laboratory and shall comply with the requirements of Section 01 45 00.15 RESIDENT MANAGEMENT SYSTEM CONTRACTOR MODE (RMS CM) and be a USACE accredited laboratory. Submit Quality Control Laboratory Qualifications for approval.

1.7 DELIVERY, STORAGE, AND HANDLING

Protect materials delivered and placed in storage, protected from the weather, soil, dust or other contaminants.

1.8 GEOTECHNICAL SITE CONDITIONS

1.8.1 Exploration

Subsurface exploratory borings and cone penetrometer test (CPT) probes and have been performed by the Government to evaluate the subsurface conditions. Approximate locations of the explorations, boring and CPT log descriptions, levee embankment and subsurface materials encountered during explorations are included in the REACH H GDR, for the convenience of the Contractor. The Government assumes no responsibility for interpretations

31 56 15 - 10 made by the Contractor from the explorations. Local variations in the subsurface materials are to be expected and, if encountered, will not be considered as being materially different within the purview of this contract. Construction verification exploration of cutoff wall depth requirements is addressed in paragraph CUTOFF WALL KEY-IN VERIFICATION

EXPLORATIONS AND MONITORING.

1.8.2 Ground Water

A description of the regional ground water condition is presented in the

REACH H GDR.

1.8.3 Knowledge of Subsurface Data

It is the Contractor's responsibility to become acquainted and satisfied as to the character, quality, and quantity of surface and subsurface materials by inspecting the site, performing additional borings as necessary for soil classification and demonstration section formulation and by evaluating information derived from the exploration work performed for this project and included in these plans and specifications. Any failure by the Contractor to become acquainted with all the available information and any other site specific conditions such as utilities will not relieve the Contractor from responsibility for properly estimating the difficulty or cost of successfully performing the work.

PART 2 PRODUCTS

2.1 GENERAL

Maintain at the job site a sufficient quantity of raw materials and other supplies such that the work can proceed uninterrupted by material shortages. If necessary, modify the VCT cutoff wall backfill design mixes to meet the requirements for permeability, continuity, and homogeneity specified in this Specification section. Undertake any additional tests necessary to assist in material selection, to verify compliance with the Specifications, and to demonstrate the characteristics of the cutoff wall.

2.2 BENTONITE

Bentonite shall be sodium cation base montmorillonite powder that conforms to API Spec 13A, Section 9. Bentonite shall be new, pulverized, high-swelling natural sodium cation montmorillonite (Premium Grade Wyoming-type bentonite or equivalent). Chemically treated bentonite will not be allowed. No bentonite from the bentonite manufacturer shall be used prior to acceptance by the Contracting Officer. All bentonite shall be subject to inspection, sampling, and verification of quality by Contractor Quality Control (QC) testing and Government Quality Assurance (QA) testing. Bentonite not meeting specifications shall be promptly removed from the site and replaced with bentonite conforming to specification requirements at the Contractors expense. Protect bentonite from moisture during transit and storage.

Provide a sample of the bentonite material used within the mix upon request from the Contracting Officer's representative. The sample shall consist of a minimum of 10 pounds of the proposed bentonite at least 5 days prior to use with certification that it meets API Spec 13A.

Submit a copy of the Bentonite Powder Manufacturer Test Results for each lot shipped to the site and a certificate of compliance stating that the

31 56 15 - 11 bentonite complies with all applicable standards.

2.3 WATER

2.3.1 Source

Refer to Section 01 50 02, TEMPORARY CONSTRUCTION FACILITIES for information on potential water supplies and the requirements that apply to providing the water supply for construction of the Project. Provide the water sources used for production and associated pH, hardness, total dissolved solids analysis (water sources used for production shall be same as trial mix). City hydrants if used by Contractor shall be identified in work plan: (1) note the locations of hydrants for use, and (2) procure appropriate permits. Abide by any and all regulations and other requirements governing such use. Include the cost of all related fees in the bid items pertinent to the Work.

2.3.2 Water Quality

The water shall comply with the standards specified below. Furnish Water Quality Test Results for water used for mixing with the slurry to assure conformance with these standards.

Property Property Requirement Test Method pH Vale 7.0 +/- 1.0 API RP 13B-1

Total Dissolved Solids <500 ppm EPA 600/4-90/027F

Oil, organics, acids, or other deleterious

<50 ppm each API RP 13B-1

Hardness <50 ppm API RP 13B-1

Water with hardness in excess of 50 ppm will be acceptable to the Government for use to construct the SB cutoff walls based on performance in the trial mix as long as the required permeability standards specified herein for the mix are achieved throughout the project.

2.4 VCT SOIL-BENTONITE MIXTURE

The procedures by which the Contractor will inject, calculate, and monitor quantities of bentonite and water shall be defined by the Results of the Demonstration Section of the successfully constructed cutoff wall.

The SB mixture shall consist of in situ soil mixed with water (both in situ and added) and bentonite to form a low permeability wall. The bentonite shall consist of either a slurry mixture or dry application with water injection as needed for the VCT method. The bentonite shall meet the requirements specified. The initial mixture used in the demonstration section shall contain a minimum of four percent bentonite by dry weight of soil. Either wet bentonite slurry or dry bentonite injection is permitted however, the final mix proportions shall be determined by the results of the required demonstration section. Based on the results of the specified demonstration section, the bentonite quantity shall be adjusted by the contractor as necessary, and as approved by the Contracting Officer to achieve the properties specified below at no additional cost to the Government. The SB mixture in the trench shall have the following

31 56 15 - 12 properties based on a 10-specimen moving (running) average.

a. Slump: The SB mixture shall have a 10-test average slump cone value of 5 inches to 7 inches determined in accordance with ASTM C143/C143M. No test result shall be less than 4 inches and no higher than 9 inches.

b. Density: The SB mixture shall have a 10-test average saturated unit weight of at least 105 pounds per cubic foot (pcf) determined in accordance with ASTM D7263. No test result shall be less than 95 pcf.

c. Hydraulic Conductivity: The SB mixture shall have 80 percent of a 10-test running average equal to 5x10-7 centimeters per second (cm/sec) or less when measured at 28 days and tested in accordance with ASTM D5084. No test shall be greater than 1x10-6 cm/sec. Any test greater than 1x10-6 cm/sec and may be retested once before rejected.

The initial design mix may be adjusted by the Contractor if necessary and if approved by the Contracting Officer based on the Results of the Demonstration Section and to adapt to changes in field conditions at no additional cost to the Government.

Submit a record of VCT injection rate and quantity of materials (bentonite and water quantities) introduced into the cutoff well including any additives utilized, and adjustments for each production shift including the date mixed and cutoff wall stations completed.

2.5 MATERIAL STORAGE FACILITY

Provide all necessary materials, equipment and personnel to store the bentonite and other additives under conditions to prevent moisture or other contaminants from mixing with the materials prior to use.

2.6 ENVIRONMENTAL PROTECTION

The raw materials and other supplies used in the construction of the VCT SB cutoff wall and any spoil disposed of shall be non-hazardous and shall comply with SECTION 01 57 20 ENVIRONMENTAL PROTECTION to prevent, and provide for abatement and control of, any environmental pollution arising as a part of the work.

2.7 DISPOSAL SITE

Cutoff wall trench excavated material and/or excess bentonite slurry that are not suitable for use per Section 31 00 00 EARTHWORK shall be disposed of off-site at the Contractor's own expense.

2.8 TRENCH PLATES

The minimum plate thickness shall be 1-1/4 inches for the specified trench width. Steel plates also known as steel plate bridging shall consist of steel designed for HS20-44 truck loading per Caltrans Bridge Design Manual.

Maintain on the steel plates a non-skid surface having a minimum coefficient of friction of 0.35 as determined by California Test Method

342. The trench plates shall extend a sufficient distance beyond the edge of the trench walls so that load transfer from the plates does not impact trench stability during curing and strength development of the wall.

31 56 15 - 13

2.9 EQUIPMENT

Furnish all necessary plant and equipment for use on this Project. Obtain and maintain at the jobsite a supply of spare critical replacement parts or backup equipment sufficient to allow the cutoff wall construction to proceed with minimum loss of time due to mechanical breakdown or equipment failure. Calibration of Scales and Flow Meters shall be provided by the Contractor.

2.9.1 VCT Excavation Equipment

The equipment shall be capable of excavating the required minimum width of trench in a single pass of the excavating equipment. The equipment shall be able to excavate a maximum of 10 feet deeper than the depth shown on the Plans. However, between Station 44+50 and Station 50+00, the equipment will not be required to excavate below the depth shown on the Plans. Provide written description on the method for verifying vertical tolerance and shall be accepted by the Government as part of the Cutoff Wall Implementation Plan submittal package.

If there is instability of the cutoff wall due to equipment excavation, repair the wall at no expense to the Government.

2.9.2 VCT Mixing Equipment

The VCT equipment used for batching and mixing the bentonite and injected water shall be capable of mixing the materials into a homogeneous mixture conforming to the contract specification requirements. Mixing equipment shall be capable of mixing the in situ trench material to provide and maintain a uniform blended cutoff wall.

The VCT equipment shall have a controlled weighing and metering system for assuring that the dry and/or wet constituents of the mixture are properly proportioned. If a dry mixture is used, the proportions and rates of injection of bentonite and any added water shall be continuously monitored and recorded. If wet bentonite slurries are pumped, appropriate mixing and storage tanks shall be provided and the slurry density, flow rates, and total volume of slurry pumped shall be obtained and reported using an electronic data acquisition system.

The rate of material use will be made available for Government inspection so that the proportions of the various mixes can be checked. Data acquisition display will be easily accessible to QA inspectors as to not interfere with Contractor's activities. At the end of each shift, submit a hardcopy output of all the data collected along with a digital record of the materials used. Digital record shall be compatible with Windows 7 for import into Microsoft Excel or other approved spreadsheet by the Contracting Officer.

2.9.3 Field Laboratory Equipment

The Contractor's field laboratory equipment for Contractor's quality control testing shall be made available for Government testing at any time and shall contain, at a minimum, the following equipment:

1. Two Marsh funnel sets

2. One standard filter press

3. Two mud balances (direct reading of density)

31 56 15 - 14

4. One slurry sampler

5. Two No. 200 sieves

6. One set of standard sieves and sieve shaker

7. One oven for moisture content

8. One scale

9. One pH meter

10. Two slump cones

2.9.4 Hauling Equipment

Earthwork related hauling equipment shall consist of pneumatic-tired vehicles with bodies suitable for the material being hauled and meeting the requirements of paragraph EQUIPMENT WEIGHT, SPEED, AND WIDTH.

2.9.5 Equipment Weight, Speed, and Width

Weight of equipment to be used on the levee crown shall be limited to a maximum gross loaded axle weight of 34,000 pounds for trucks. For tracked vehicles, the maximum ground pressure allowed is 2,500 pounds per square foot. The maximum weight of the excavator shall not exceed 300,000 pounds without prior approval of the Contracting Officer and after evaluation of the Contractor of the effect on levee stability by use of stability analyses. The maximum operating speed of all equipment used on the levee crown or levee toe roads shall be 15 mph. The maximum overall width of equipment used on the levee shall be limited 18 feet.

2.10 CONSTRUCTION STAKING

Provide, install and maintain all layout and necessary construction staking to locate the cutoff wall centerline within the alignment of the cutoff wall and the cutoff wall length as shown on the Plans. Surveyor's caps, appropriately identified to include survey control number and name of survey company and mounted on a 2-inch diameter, 2-foot-long steel pipe, driven into the ground, shall be provided at each end of the cutoff wall.

Wooden stakes shall be placed along the cutoff wall centerline at 100-foot maximum intervals between the ends. Coordinates and elevations shall have units consistent with the Plans. Temporary flagging shall be provided in 10 foot intervals. A tabulated list containing survey control numbers, grid coordinates, project station number, and elevations shall be submitted to the Government within five working days of completing each heading and a summary list at the completion of all survey controls. The beginning and ending of the cutoff wall and utility crossings shall be identified on this list. Survey construction control staking shall be performed by a California licensed surveyor and all survey data shall be stamped by the licensed surveyor.

2.10.1 Initial and Final Elevation

The survey caps at ends of the cutoff wall shall be surveyed to establish initial elevation and final elevation to an accuracy of plus or minus 0.1 foot and these stakes shall be maintained and protected from damage or movement throughout the work. Submit a report to the Government for the cutoff wall installation showing any settlements that occurred and also indicating the final restored levee crown elevation in comparison to the pre-construction elevation. The cutoff wall stations shall have the theoretical maximum elevations of the bottom of the cutoff wall established, and furnished as part of the submittal. A system for locating stations along the cutoff wall alignment and relating them to the plans shall be established by the Contractor and submitted to the Government for

31 56 15 - 15 approval.

2.11 PERMANENT METAL MARKER STAKES

Upon completion of the cutoff wall installation, permanent metal markers stakes meeting the requirement of Type L-1 Object Markers of CA MUTCD shall be placed. In-lieu of the yellow reflective sheeting referenced in the Type L-1 Object Markers, the station location and levee mile of the cutoff wall ends shall placed on the marker. The markers shall be surveyed in at the corresponding projected station location and installable at the landside toe of the levee at the cutoff wall ends.

PART 3 EXECUTION

3.1 GENERAL

The cutoff wall shall be constructed to the elevations, lines, grades, and cross sections shown in the plans and in accordance with these specifications, unless otherwise directed. The Contracting Officer may modify the dimensions and quantities of the work as determined necessary.

3.1.1 VCT Cutoff Wall Implementation Plan

Submit a VCT Cutoff Wall Implementation Plan that includes the required key-in verification exploration plan, construction schedule, sequence of operations, equipment date, and quality control program details.

Describe the general work sequence and layout of operations, work hours, and number of headings. Include scale drawings which depict VCT preparation and storage areas in the layout of operations. The plan shall describe Contractor equipment, method of trench excavation, disposal of excavated material, bentonite preparation and placement, and site clean-up.

Detail procedures for locating the cutoff wall in the field and confirming that the cutoff wall is plumb. Provide data and operations manuals on the trench depth measuring equipment. Include a detail plan and procedure for monitoring and addressing slurry loss through the levee.

Describe the quality control program including quality control equipment, testing and sampling equipment, and all required test procedures, sample test forms for reporting test results, onsite and/or offsite laboratory proposed for use, sample storage on site and method of transporting samples to laboratory. Include a reporting schedule for completed VCT mix density tests, gradation tests, permeability tests, and offsite independent laboratory. The implementation plan will be revised as necessary following the interpretation of results and successful completion of the demonstration section.

The implementation plan shall include the data on the equipment used in the construction of the cutoff wall; equipment used to obtain QA samples of the completed cutoff wall; and equipment used in the Contractors quality control testing and measuring. This data shall include mixing equipment, storage and delivery equipment and metering and weighing systems.

Procedures shall include methods for locating the cutoff wall in the field and confirming that the cutoff wall is in vertical tolerances. Data on equipment used for measuring the trench depth shall be submitted as well as any applicable operations manual, and information on equipment and procedure to obtain bulk samples of the cutoff wall material of the wet bulk VCT SB material from within the trench.

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3.2 SITE WORK

Furnish all plant, equipment, labor, and materials required to construct the VCT SB cutoff wall as shown on the Plans and specified herein, except that the Contracting Officer may at any time direct changes to the wall depth and length to accommodate conditions encountered in the field.

3.3 WORKING SURFACE

Accomplish trench construction from the working surface as shown on the Plans and defined in paragraph DEFINITIONS. The working surface as shown on the Plans shall constitute the top of the cutoff wall for the purpose of measurement and payment.

3.3.1 Construction Staking

Provide, install, and maintain all temporary benchmarks, layout staking and necessary construction staking to locate the centerline of the wall.

Flagging shall be used to show the stationing every 10 feet. Survey construction control staking shall be performed by a Licensed Surveyor or Registered Professional Civil Engineer authorized to perform surveying in California. All survey data shall be stamped by the surveyor/engineer.

3.3.2 Construction of Working Surface

Construct a working surface as needed to achieve the limits shown on the Plans. 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 subgrade and compaction requirements are described in Section 31 00 00 EARTHWORK. Upon completion of the cutoff wall installation, the levee shall be restored to final alignment lines and grade in accordance with Section 31 00 00 EARTHWORK.

3.4 VCT SB CUTOFF WALL CONSTRUCTION

3.4.1 General

The excavation shall begin from the working surface and shall provide a vertical (within 2 percent) continuous 30 inch minimum width trench to the required depth along the centerline of the excavation. The equipment shall have a configuration and orientation that reduces live load and dead load surcharge to an amount that will maintain stability of the trench. Steel plates shall be used to bridge and distribute loads over the cutoff wall.

Construct the trench using continuous excavation or other methods approved by the Contracting Officer. When trench excavation overlaps into previously constructed SB cutoff wall backfill, the excavation shall extend a minimum of 5 feet into this contracts previously constructed cutoff wall backfill at all depths to ensure continuity of the completed SB cutoff wall. Any excavated section of completed cutoff wall shall be remixed at no additional expense to the Government.

3.4.2 Cutoff Wall Key-In Verification Explorations and Monitoring

Pre-excavation cutoff wall key-in verification explorations at a maximum of 150 feet center along the alignment of the cutoff wall shall be implemented by the Contractor. The verification explorations may include those existing, design-phase borings presented in the REACH H GDR with sufficient information at the cutoff wall key-in elevation and new borings. New

31 56 15 - 17 borings shall be initiated before start of the cutoff wall excavation and shall stay at least 5 days ahead of planned excavation. The borings shall be advanced to a depth of 10 feet below the planned bottom of the cutoff wall as identified on the Plans. Continuous soil sampling from a stable borehole shall be performed from 5 feet above the planned bottom of the cutoff wall to 10 feet below the planned bottom of the cutoff wall.

Contractor will be required to obtain all necessary permits for these explorations. If a key-in layer is deeper than planned, the bottom of the boring will be advanced, as per Contracting Officer's directions.

The Contracting Officer's representative will be onsite during excavation and mixing of VCT construction and will monitor the trench during excavation for the full depth of each segment.

3.4.3 VCT Demonstration Section

The location of the demonstration section will be selected in conjunction with the Contracting Officer and in an area where a design phase boring exists. Prior to starting production cutoff wall construction, construct a cutoff wall demonstration section to verify that the performance criteria in paragraph VCT SOIL-BENTONITE MIXTURE are met. Submit a Demonstration Section Design and Implementation Plan for approval by the Contracting Officer. A minimum 100 foot linear demonstration section of cutoff wall will be constructed to verify the demonstration section meets minimum project performance criteria prior to production cutoff wall construction.

A proposed demonstration section design and implementation plan will be prepared and submitted by the Contractor including proposed: batching and monitoring procedures for inspection of bentonite and water usage, rate of advancement, chain rotation, and target demonstration section including percentage and rate of bentonite and water injection.

Submit a report summarizing the procedures and results of the preconstruction VCT demonstration section. The report shall include advancement rate, chain rotation speeds, a description of materials used (including additives), mix proportions, water ratio, densities, gradation and classification of mixed materials, calculation relating to injection and mixing rate with minimum bentonite cement by weight of dry soil, slump of mixed materials, and permeability of a minimum of five samples of the proposed VCT cutoff wall from the top, middle, and bottom. The calculation shall show how the injection and procedure ensures mixing of minimum bentonite, as per the approved design mix. The demonstration section shall consist of a 100-foot-long linear segment of completed SB cutoff wall. At least one key-in verification exploration shall be located in the demonstration section. The initial SB mix shall contain a minimum of four percent bentonite by dry weight. The documentation and testing of the demonstration section shall be in accordance with paragraph QUALITY CONTROL TESTING. Following completion of the SB cutoff wall demonstration section, stand down until the laboratory test results demonstrate that the performance and Demonstration Section Test Report is approved by the Contracting Officer. As a result of the findings of a successful demonstration section, the VCT Cutoff Wall Implementation Plan shall be revised as necessary in accord with paragraph SB CUTOFF WALL IMPLEMENTATION

PLAN.

3.4.4 Monitoring

Monitor and adjust the cutter post speed as necessary during the wall excavation and mixing process. All metering and weighing equipment shall be calibrated at the beginning of the cutoff wall installation work and

31 56 15 - 18 again at the 50 percent project completion point. The VCT Contractor shall submit the monitoring results to the Contracting Officer at the end of each day.

3.4.4.1 Cutter Chain Rotation Speed and Advancement Rate

The cutter speed and advancement rates shall be as established by the Contractor during the demonstration section and shall be adjusted as needed to achieve adequate mixing. If the cutter speed and advancement rate varies by more than ten (10) percent from the parameter established in the demonstration section, the Contracting Officer may require additional testing to verify acceptable results at no additional cost to the Government.

3.4.4.2 Bentonite Injection Rate

The quantity of bentonite (dry or slurry) injected shall be in accordance with the design established during the demonstration section. The bentonite injection rate shall be constantly monitored, calculated, and controlled.

For production quality control, the real time monitoring of the bentonite injection rate shall be performed. The injection rate shall meet the minimum rate established by the demonstration section.

3.4.4.3 Bentonite Injection Modifications

The Contractor may request to modify the established demonstration section and injection ratio. All modifications are subject to Government review, and the Contracting Officer may request additional Quality Control testing to verify acceptable results at no additional cost to the Government.

3.4.5 Vertical Tolerance

The VCT cutoff wall shall not deviate from vertical more than two percent of the depth of wall. The vertical deviation will be measured using an approved procedure. Deviations from vertical of more than two percent shall be cause for rejection for that portion of the cutoff wall. Reconstruction of an VCT cutoff wall segment because of excess deviation from vertical shall not be the cause for additional compensation.

3.4.6 Bottom Depth

The cutoff wall shall be excavated to the depth and grade shown on the Plans as verified by the explorations described in paragraph CUTOFF WALL KEY-IN VERIFICATION EXPLORATIONS AND MONITORING. The Contracting Officer may direct the Contractor to modify the depth based on the results of the verification explorations and/or field observations during excavation. The bottom elevation of the cutoff wall may vary from 5 feet above to 10 feet below the elevation shown on the Plans without a contractual change order.

However, between Station 44+50 and Station 50+00, the bottom elevation of the cutoff wall will not be required to extend deeper than shown on the Plans.

3.4.7 Trench Stability

Be responsible for ensuring and maintaining the stability of the excavated trench at all times for its full length and depth. Control surcharges from all excavation and backfilling equipment, waste, berm construction, and any other loading situations that may affect trench stability. It is the Contractor's sole responsibility to ensure that any stockpiles and traffic

31 56 15 - 19 do not affect trench stability. In the event of failure of the trench walls, notify the Contracting Officer. Corrective actions will be determined and approved by the Contracting Officer and may include re-mixing the affected area and repairing damaged sections of the levee embankment. Corrective actions associated with trench sidewall instability due to loading of the trench sidewalls shall be at the Contractor's own expense. Take corrective action to prevent further deterioration.

3.4.8 Continuity of Cutoff Wall

Cutoff wall elements shall be excavated maintaining chain rotation and excavator advancement speed to ensure a continuous, thoroughly mixed cutoff wall. At each new shift or for work stoppage greater than 12 hours, the completed cutoff wall trench shall be reworked and excavated at a distance of 10 feet at all depths. When trench excavation overlaps into previously completed cutoff wall, the excavation shall extend a minimum of 10 feet into the previously completed VCT cutoff wall at all depths before initiating new construction.

3.4.9 Top of Cutoff Wall

After completion of a VCT work segment (shift, day, etc.), maintain the VCT mix to within 1 foot of the ground surface. After initial setting of the VCT mix, remove any free water, all sloughed trench sidewall material, or disturbed mix material from the top of the cutoff wall, and add fresh VCT mix to the top of the cutoff wall. Repair any depression that develops within the completed cutoff wall area, with additional VCT mix material.

Place a temporary plastic sheeting cover over the top of the cutoff wall to prevent desiccation after trench is topped off. The temporary plastic sheeting shall be removed prior to placing the temporary soil cap. See paragraph CUTOFF WALL PROTECTION for additional information relating to loads on the cutoff wall and equipment crossings.

3.4.10 Temporary Cap

A temporary cap shall be placed within 48 hours of SB cutoff wall construction over each 100 foot section along the trench. The temporary cap shall be constructed using levee fill material as per Section 31 00 00 EARTHWORK and placed without compactive effort. The temporary cap shall be removed no sooner than 28 calendar days after placement, except that a shorter time may be allowed by the Contracting Officer based upon monitoring of the actual cutoff wall settlement. The temporary cap shall be 2 feet thick and cover the trench as shown on the Plans. If any depression develops within the completed SB cutoff wall, it shall be repaired by placing additional material. This material shall be SB mix if the depression is observed during cutoff wall construction and levee fill material if the depression is observed after placement of the temporary cap. Heavy construction equipment and machinery shall only be driven over the constructed SB cutoff wall at approved heavy-equipment crossing points that are bridged by metal plates meeting specifications to support the equipment weights. Contractor will avoid heavy equipment loading adjacent to or on the temporary cap until approved by the Contracting Officer based on the settlement plate monitoring.

3.4.11 Settlement Plate Installation and Monitoring

Settlement plates shall be installed by the Contractor at 500-foot spacing.

The first settlement plate shall be installed within 50 feet of the toe of the initial cutoff wall construction. Each settlement plate shall be

31 56 15 - 20 installed as soon as the wall has reached sufficient strength to support

it. The settlement plate locations shall be adjusted at the discretion of the Contracting Officer as needed based on construction activities.

Settlement plate monitoring surveys shall be completed daily for 28 days. A longer or shorter settlement monitoring period may be determined by the Contracting Officer based on the settlement results. Monitoring surveys shall be accurate to 0.01 foot and shall be accomplished by performing a closed loop level survey beginning and ending on known control points.

Construction laser levels may not be used for settlement plate monitoring surveys. Monitoring surveys shall be performed by a licensed Land Surveyor or Civil Engineer authorized to perform surveying in California and shall be provided to the Contracting Officer within 48 hours after completion of the settlement plate monitoring survey. Levee embankment operations may begin at the end of the settlement monitoring period, as determined by the Contracting Officer. Costs for installing, monitoring, and removing settlement plates shall be included in the Contractor's unit cost for cutoff wall installation.

3.4.12 Removal of Temporary Cap and Settlement Plates

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