city of manhattan beach department of public works

City of Manhattan Beach

Department of Public Works

Engineering Division

3621 Bell Avenue, Manhattan Beach, CA 90266

Phone: (310) 802-5350 Fax: (310) 802-5351 TDD: (310) 546-3501

Addendum No. 3 of 2 Project #1243-20

CITY OF MANHATTAN BEACH

ADDENDUM NO. 3

8 MG Peck Reservoir Replacement Project

Project No. 1243-20

This Addendum shall take precedence over any conflicting information contained either in the

plans, specifications or advertisement of Notice Inviting Bids for the 8 MG Peck Reservoir

Replacement Project. Bidders shall incorporate the information contained in this Addendum in

their bids, conform to all of the instructions contained herein in the preparation of a bid, and

shall sign and submit this Addendum as a portion of the Contractor’s Proposal as an indication of

understanding and compliance with this Addendum.

The following items are clarifications related specifically to the Mechanically Stabilized Earth

(MSE) Wall System.

1. Section 32 32 35 – MSE Wall System. Amend Section 32 32 35 of the Special

Technical Provisions, and replace entire section with the attached revised

Section 32 32 35 – Mechanically Stabilized Earth (MSE) Wall System.

2. BidSync Question #15 – MSE Wall System Non-Battered Facades. Question: Specification Section 32 32 35 - MSE Wall describes segments of wall requiring non-battered facades within 1.1.A.2 and 1.4.D.7.k. These areas were not observed on the plans. Please clarify the requirements. Response: Specification Section 32 32 35 - MSE Wall System has been updated. The revised performance specification is attached to Addendum No. 3.

This Addendum is approved by:

Prem Kumar, City Engineer Date

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6/01/2020

City of Manhattan Beach

Department of Public Works

Engineering Division

3621 Bell Avenue, Manhattan Beach, CA 90266

Phone: (310) 802-5350 Fax: (310) 802-5351 TDD: (310) 546-3501

Addendum No. 3 of 2 Project #1243-20

A SIGNED COPY OF THIS ADDENDUM MUST BE ATTACHED TO THE BID.

I hereby acknowledge that the information contained in this addendum has been included in the

bid submitted for this project.

COMPANY NAME SIGNATURE DATE

STANTEC- APRIL 2020 MECHANICALLY STABILIZED EARTH (MSE) WALL SYSTEM MANHATTAN BEACH- PECK RESERVOIR REPLACEMENT PROJECT PAGE 32 32 35-1

SECTION 32 32 35 - MECHANICALLY STABILIZED EARTH (MSE) WALL SYSTEM

PART 1 -- GENERAL

1.1. APPLICATION

A. This is a performance specification. The work will require the CONTRACTOR to design, furnish, and construct a mechanically stablilized earth (MSE) wall system, including leveling pad, soil reinforcement, drainage fill, reinforced backfill, and incidental materials required for MSE wall system construction to the lines and grades shown on the CONTRACT DOCUMENTS and as specified herein.

B. The MSE wall system will consist of:

1. Battered walls

2. Plantable wall faces with a minimum coverage of 30%

C. The MSE wall system will include segments with:

1. Interfaces with cast-in-place concrete structures

2. Vertical interfaces with metal picket fences

3. Segments with a brow-mounted guard rail

4. Segments with a metal picket fence behind the top layer of block

1.2. REFERENCE

A. General

1. The publications listed below form a part of this specification to the extent referenced.

2. Where a date is given for reference standards, the edition of that date shall be used. Where no date is given for reference standards, the latest edition available on the date of Notice Inviting Bids shall be used.

B. American Society for Testing and Materials (ASTM)

1. Segmental Retaining Wall (SRW) Units

a. ASTM C90, Standard Specification for Load Bearing Concrete Masonry Units

b. ASTM C140, Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units

c. ASTM C1372, Standard Specification for Dry-Cast Segmental Retaining Wall Units

2. Geosynthetics Reinforcement

a. ASTM D1388, Standard Test Method for Stiffness of Fabrics

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ADDENDUM NO. 3 ISSUED 6/01/2020


b. ASTM D4218 Standard Test Method for Determination of Carbon Black Content in Polyethylene Compounds by the Muffle-Furnace Technique

c. ASTM D5262, Standard Test Method for Evaluating the Unconfined Tension Creep and Creep Rupture Behavior of Geosynthetics

d. ASTM D6637, Standard Test Method for Determining Tensile Properties of Geogrids by the Single or Multi-Rib Tensile Method

e. ASTM D6638, Standard Test Method for Determining Connection Strength Between Geosynthetic Reinforcement and Segmental Concrete Units (Modular Concrete Blocks)

f. ASTM D6706, Standard Test Method for Measuring Geosynthetic Pullout Resistance in Soil

3. Soils

a. ASTM D422, Standard Test Method for Particle Size Analysis of Soils

b. ASTM D1556, Standard Test Method for Density and Unit Weight of Soil in Place by the Sand-Cone Method

c. ASTM D1557, Standard Test Method for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lb/cu ft. [2,700 kN-m/cu.m.])

d. ASTM D2487, Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)

e. ASTM D3080, Standard Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions

f. ASTM D4318, Standard Test Methods for Liquid Limit, Plastic Limit and Plasticity Index of Soils

g. ASTM D4829, Standard Test Method for Expansion Index of Soils

4. Drainage Pipe

a. ASTM D1248, Corrugated Plastic Pipe

b. ASTM D3034, Standard Specification for Type PSM Poly Vinyl Chloride (PVC) Sewer Pipe and Fittings

c. ASTM D4475, Horizontal Shear Strength of Pultruded Reinforced Plastic Rods

C. Geosynthetic Research Institute (GRI)

1. GRI-GG2, Geogrid Junction Strength

2. GRI-GG4; Determination of Long-Term Design Strength of Geogrids

3. GRI-GG5, Determination of Geogrid (soil) Pullout

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4. GRI-GG7, Carboxyl End Group Content of PET Yarns

5. GRI-GG8, Determination of the Number Average Molecular Weight of PET Yarns Based on Relative Viscosity Value

D. National Concrete Masonry Association (NCMA)

1. NCMA SRWU-I Test Method for Determining Connection Strength of SRW

2. NCMA SRWU-2 Test Method for Determining Shear Strength of SRW

E. California Department of Transportation (Caltrans)

1. Caltrans Corrosion Guidelines

2. Caltrans California Test Method (CTM) 417, Test Procedures for Determining Water-Soluble Sulfate Content

3. Caltrans California Test Method (CTM) 422, Test Procedures for Determining Water Soluble Chloride Content

4. Caltrans California Test Method (CTM) 643, Procedures for Determining Resistivity and Soil pH

5. Caltrans Seismic Design Criteria

6. Caltrans' A Technical Report to Accompany the Caltrans California Seismic Hazard Map 1996 (Based on Maximum Credible Earthquakes)

7. Caltrans California Seismic Hazard Map 1996, Based on Maximum Credible Earthquakes (MCE)

F. Engineering Design Standards

1. United States Department of Transportation, Federal Highway Administration (FHWA)

a. FHWA-NHI-10-024, "Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes - Volume I", 2009

b. FHWA-NHI-10-025, "Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes - Volume II", 2009

c. FHWA-NHI-09-087, “Corrosion/Degradation of Soil Reinforcements for Mechanically Stabilized Earth Walls and Reinforced Soil Slopes", 2009

2. National Concrete Masonry Association (NCMA)

a. NCMA Design Manual for Segmental Retaining Walls

b. NCMA Segmental Retaining Walls-Seismic Design Manual

3. American Association of State Highway and Transportation Officials (AASHTO)

a. AASHTO Standard Specifications for Highway Bridges

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G. Planting

1. The CONTRACTOR shall reference Specification Section 32 93 00 Landscaping for seeding and planting within the MSE Wall system façade.

1.3. DEFINITIONS

A. Earth Materials

1. Reinforced Backfill Zone, Reinforced Backfill, Reinforced Soil Zone, Reinforced Fill Geogrid Zone, Compact fill materials in which the geogrid reinforcement are placed as shown on the Drawings. The source of the reinforced backfill is derived from the earth materials indicated in Paragraph 1.4C below.

2. Foundation Soil-Earth materials beneath the entire MSE wall systems.

3. Alluvium Unconsolidated non-unindurated topsoil materials not on the surface of the slope.

B. Mechanically Stabilized Earth (MSE) Wall System-Composite retaining wall primarily consisting of MSE wall facing, compacted soils reinforced with multiple layers of geogrid reinforcements spaced at regular vertical height/depth intervals, leveling pad, and drainage layers.

C. MSE Wall Facing-Primarily modular concrete facing units made from Portland cement, water, and mineral aggregates for use in the construction of MSE wall system. Other types of wall facing may also be considered.

D. Drainage Fill, Drainage Layer-Drainage aggregate that is placed within and behind the segmental concrete unit, and underneath and behind the MSE wall system.

E. Soil Reinforcement: Geosynthetic Reinforcement, Geogrid Reinforcement-Geosynthetic reinforcement consisting of geogrids manufactured specifically for use as horizontal reinforcement layers, in order to add tensile strength to a compacted soil mass, thereby providing a stabilized, competent, and reinforced soil structural material.

F. Base Leveling Pad, Leveling Pad-Level compacted gravel or unreinforced concrete pad upon which the first course of wall facing segmental concrete units is placed.

1.4. DESIGN REQUIREMENTS

A. The CONTRACT DOCUMENTS and Specifications include the minimum configuration and requirements for the design and construction of a plantable MSE wall system, which are not intened to be the final design of the MSE system. The final design is to be provided by the CONTRACTOR. The MSE wall system configuration shown on the CONTRACT DOCUMENTS represents minimum embedments, wall heights, and geogrids lengths which are consistent with a battered wall design. The CONTRACTOR and its MSE wall design consultants shall be responsible for detailed final design of the MSE systems, subject to approval of the ENGINEER and shall be fully responsible for the adequacy of the designed and constructed MSE wall systems. The CONTRACTOR’s final design shall include the selection of the MSE wall system, the wall facing unit and the associated batter of the wall system, which maybe result in greater wall embedments wall heights, and geogrid lengths than those shown on the project drawings for the minimum configuraton. The CONTRACTOR is advised to review all available MSE wall systems to determine the most optimum system for this

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project, consistent with project design and constructions criteria and requirements, and their planned means and method of constructions.

B. Design Method:

1. Design of MSE wall systems using geogrid reinforcement shall be in accordance with the FHWA Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines and the AASHTO Standard Specifications for Highway Bridges.

C. Reinforced Fill and Foundation Design Parmeters

1. The following soil parameters shall be used by CONTRACTOR for design of the MSE wall system:

Dry Unit Weight (pcf)

Friction Angle, (degrees)

Cohesion (psf)

Onsite Excavated Soil (1)

Reinforced Backfill 117 30 - 37(2) 300

Retained Soil 117 30 - 37(2) 300

Foundation Fill 117 30 - 37(2) 300

1. Onsite excavated soil from the project area of can be used as fill in the retained soil,

reinforced soil, and the foundation fill zones.

2. Contractor is to fully review the Geotechnical Report and understand the design

parameters set forth therein.

2. Ensure that the internal friction angle (Φ) for the reinforced fill is not less than 30 degrees. Use the data listed in the table above for design purposes. Ignore cohesion of the reinforced fill material when designing the MSE wall system.

D. Performance Requirements

1. Unless otherwise indicated below, the MSE wall system design methods shall be performed in strict compliance with Paragraph 1.4B above and the following:

The MSE wall system should meet or exceed the following criteria:

• Design Life: 75 years • A traffic load surcharge consistent with AASHTO HS-20 loading shall be

considered.

2. Structural Performance: Provide MSE wall systems capable of supporting the static and seismic loads due to the lateral earth pressures resulting from the grades and configurations indicated on the Drawings and all surcharge loads. See Project Geotechnical Report for lateral earth pressure recommendations.

3. Seismic Performance: The seismic design of MSE systems shall be in accordance with the FHWA Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines and the AASHTO Standard

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Specifications for Highway Bridges. The site design peak ground acceleration (PGA) is 0.6g and the site is a Site Class D. See Project Geotechnical Report for additional seismic design parameters.

4. Long-term differential settlement of the wall facing shall not exceed 1/4 inch over 40 feet.

5. The design life of the MSE wall systems shall be 75 years.

6. The MSE wall embedment depth shall conform to the parameters below:

Minimum MSE Wall Embedment Depth

Slope in Front of Wall Minimum Embedment Depth

All Geometries

Per properly substantiated

analysis that is also in conformance

with manufacturer’s standards.

Horizontal or slopes flatter than 3H:1V Wall Height/20 Flatter than Horizontal but flatter than 2H:1V Wall Height /10

2H:1V Wall Height /7

1¾ H:1V Wall Height /6

1½ H:1V Wall Height /5

Steeper than 1½ H:1V (Wall Height /5) + 1

a. The inclination of slope in front of the MSE wall system is the average

inclination of the slope that descends vertically a height of 30 feet from the point where the existing slope surface intercepts the wall facing segmental concrete units.

b. The embedment depth shall be taken as depth below the compacted fill grade in front of the wall, or depth below contact of the bottom of the colluvium and the top surface of the natural undisturbed soil materials to the top of the leveling pad.

c. The embedment depth for any section of MSE wall system shall apply to the entire graded foundation area of the MSE wall system.

d. The bearing capacity for the footings of the MSE wall system shall be based on the earth material parameters specified in Paragraph 1.4C of this section and the gradient of the actual descending slope in front of the wall. Industry standard accepted methods of analyses shall be used, including but not limited to, the AASHTO Standard Specifications for Highway Bridges. The bearing capacity shall subtract the effect of the earth material overburden from the elevation at the bottom of footing

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upward to the surface of the lowest adjacent grade, in order to obtain a net bearing capacity value. The allowable net bearing capacity can be increased by one-third for short-duration loads.

7. In addition, the CONTRACTOR shall incorporate the following recommendations into the MSE wall system design:

a. Incorporate traffic barriers and backslope loadings as shown on the Drawings.

b. Include all surcharge loads, including traffic load.

c. Geogrid reinforcement lengths shall be determined by the CONTRACTOR based on a properly substantiated analysis and in conformance with the manufacturer’s recommendations.

d. Provide continuous, 100 percent geogrid reinforcement coverage at each reinforcement layer (no gaps).

e. Use a spacing between vertically adjacent geogrid reinforcement layers that equals the multiples of the actual (not nominal) MSE wall facing unit height. The vertical spacing of the geogrid reinforcement shall not be less than 16 inches, and not exceed 24 inches.

f. Provide a vertical space of 5 feet maximum between the top layer of the geogrid reinforcement and the surface of the asphalt concrete pavement to allow installation of buried utilities as shown on the Drawings. A miminum of 4 inches of soil cover shall be provided between the top of the geogrid reinforcement and the lowest part of any buried utility.

g. Include hinge height for MSE systems with >10° of batter.

h. Include a horizontal bench not less than 4 feet in width measured from the face of the MSE system as shown on the Contract Drawings.

i. For segments of the MSE Wall system where CONTRACT documents denote a plantable façade include planter cells that cover minimum 90-percent of the total exposed surface of the MSE wall systems and are evenly distributed across wall surface.

j. Comply with the requirements of the manufacturers of the wall facing units. In the event of a conflict between any requirements of the manufacturers of the wall facing units and the requirernent of the FHWA, NCMA, or AASHTO design methodology, the more stringent requirements shall apply.

k. A battered MSE wall system is to be consistently applied across the area indicated to consist of an MSE wall system.

l. Design submittals not meeting the design criteria specified herein will be rejected in their entirety until complete compliance is achieved.

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1.5. SUBMITTALS

A. The CONTRACTOR shall submit design calculations and working drawing of the MSE wall systems for review and approval by the ENGINEER prior to purchase of materials and construction of the MSE wall system, including execution for MSE wall system. This submittal shall be provided to the City of Manhattan Beach Plan Check for review and comment.

1. The design calculations and the working drawings shall incorporate all design requirements listed in Paragraph 1. 4 above. The design calculation shall clearly list the design assumptions, references used, and all design and input parameters used, including but not limited to, configuration of MSE system, soil strength properties, lateral earth pressures (Coulomb or Rankine as applicable), surcharge loads, geogrid parameters (type and material, strength, length, spacing, interaction parameters, reduction factors, uncertainty safety factor, connection strength), and wall facing unit parameters (geometry, weight, connection), and ground acceleration.

2. The working drawings shall include, but not be limited to, the following:

a. Plan and profile of the proposed MSE wall systems, including elevation views of each wall, cross sections, embedment depths, and all details, dimensions, and quantities necessary to construct the MSE systems, with station numbers.

b. Configuration of the MSE wall systems, including batter of the segmental concrete units, leveling pad, reinforced backfill, retained soils, foundation soils, lengths and spacing’s of geogrid reinforcements, and pipes and internal drainage fill/geocomposite drainage layer. The positions of the traffic barriers, buried utilities, pavement, and aggregate base shall also be shown on the submitted working drawings.

c. Placement of geogrid reinforcements on curves.

d. Connection details.

e. The planter cell layout and design.

f. Dimensions, spacing, tolerances, and general pattern of construction of MSE wall systems with respect to the finish grades of the roadway.

B. MSE wall system design calculations, working drawings, and the shop drawings shall be prepared, signed and stamped by a civil or geotechnical engineer currently registered in the State of California. The working drawings shall include plan and elevation views of each walls, cross sections and all details, dimensions and quantities necessary to construct the wall systems.

C. Products

1. Product literature indicating specifically which MSE wall facing units and planters’ cells are proposed for use on the project including color, and face style and texture. This shall include manufacturer's product data and recommended installation and testing procedures for the segmental concrete units. Two sample blocks of the wall facing unit, two sample planter cells, and two sample

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pins or rods for unit alignment/connection proposed for use (if any) shall also be submitted.

2. Product literature indicating specifically which geogrid reinforcements are proposed for use on the project. This shall include manufacturer's product data, recommended installation and testing procedures, and the design properties for the geogrid reinforcements. Two sample geogrids proposed for use shall also be submitted.

3. Documentation for the MSE wall facing units and geogrid reinforcement demonstrating compliance with the requirements of these specifications including but not limited to MSE wall facing unit compressive strength and absorption; wall facing unit-soil reinforcement connection and shear and design parameters; and geogrid reinforcement strength.

4. Manufacturers' certifications that the MSE wall facing units and geogrid reinforcements are compatible with each other and meet the requirements of these specifications.

D. The CONTRACTOR's methodology and equipment to be used for the installation of the wall facing units and geogrid reinforcements, including procedures and sequencing to be used for the placement and compaction of fill materials surrounding the wall facing units and geogrid reinforcements.

E. The CONTRACTOR's methodology on the storage and handling of all materials, including storage site.

F. CONTRACTOR's certifications as indicated in Paragraph 1. 6A below.

1.6. QUALITY ASSURANCE

A. The CONTRACTOR shall certify that:

1. The specific MSE wall system proposed for use on these projects has been successfully used on a minimum of five similar projects and has been successfully installed on a minimum of 1,000,000 square feet.

2. The CONTRACTOR, the CONTRACTOR’s MSE wall system design engineer, and the CONTRACTOR's field construction superintendent each have a record of successful completion of at least 200,000 square feet of MSE wall systems. The CONTRACTOR, the CONTRACTOR’s design engineer of the MSE wall system, and the CONTRACTOR's field construction superintendent shall each provide contact names and telephone numbers for three successfully completed projects with a total minimum 25,000 square feet. At least one of these references shall be for work performed jointly by the CONTRACTOR, the design engineer of the MSE wall system, and the CONTRACTOR's field construction superintendent.

3. The CONTRACTOR has received certification for the construction of the proposed MSE wall system or has received an industry certification for construction of these types of wall systems.

B. Following completion of construction the MSE wall systems, the CONTRACTOR’s design engineer shall provide a written certification that, based upon the design engineer's review of site conditions, installation procedure and records, and test data,

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the constructed MSE wall systems have been constructed in accordance with his design.

1.7. DELIVERY, STORAGE AND HANDLING

A. The CONTRACTOR shall check all materials upon delivery to assure that the proper type, grade, color and material certification have been received.

B. The CONTRACTOR shall store and handle all materials in accordance with the manufacturer's recommendations.

C. The CONTRACTOR shall protect all materials from deterioration or damage due to moisture, temperature change, sunlight, corrosion, breaking, or other causes. Damaged materials shall not be incorporated into the work.

PART 2 -- PRODUCTS

2.1. WALL FACING UNITS

A. Manufactured in accordance with ASTM C1372 with a minimum 28-day compressive strength of 3,000 psi, maximum moisture absorption of 8 percent, and a minimum weight of 70 pounds per block. MSE wall facing units finish and appearance shall be per ASTM Cl372. Color shall be Buff/Tan. The color shall be approved by the OWNER prior to purchase of units. The face finish shall be a smooth finish. The segmental concrete units to be used in the construction shall match the color, face finish, and dimensions for height, width, depth, and batter as shown on the reviewed and approved design calculations and plans.

1. Acceptable segmental concrete unit products: Verdura 40, 60, and 60W; or approved equal.

B. All wall facing units shall be sound and free of chips, cracks or other imperfections that would interfere with the proper placing of the units or significantly impair the strength or permanence of the construction. Any chips, cracks or other imperfections shall fall within the guidelines specified in ASTM Cl372.

C. All wall facing units shall not differ more than 1/8 inch in accordance with ASTM Cl372 and as measured in accordance with ASTM Cl40.

D. Cap cohesive shall meet the requirements of the manufacturer of the MSE wall facing units.

E. Pins and rods used to connect the geogrids to wall facing units shall consist of a non-degrading polymer or galvanized steel, shall be made specifically for the connection of geogrids to the wall facing units, and shall follow the recommendation of the wall facing unit manufacturer. Wall facing units with a lip or other type or unit protrusion/lug/heel to connect the geogrids by friction, wedging or interlocking between the wall facing units shall not be allowed.

F. The planter cells shall have at least 0.25 cubic feet of colume, and the layout of the cells shall not exceed 32 inches maximum space between any two cells (horizontally and vertically) as measured from the center of each cell. Acceptable planter cell unit products are Verdura 40, 60, and 60W, or equal.

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G. The modular block wall system shall be designed to accept a drip irrigation system. If the modular block wall system cannot accept a drip irrigation system then the CONTRACTOR and block wall supplier shall design an appropriate irrigation system.

2.2. SOIL REINFORCEMENT

A. Soil reinforcement shall consist of geogrids manufactured for soil reinforcement applications in MSE wall construction. The geogrid reinforcement evaluation (type, strength, and placement) shall be in accordance with the FHWA Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines and the AASHTO Standard Specifications for Highway Bridges. The specified design shall be determined by the CONTRACTOR's MSE wall system design engineer. Detailed test data shall be submitted to the Engineer for approval prior to construction, and shall include tensile strength (ASTM D6637), creep (ASTM D5262), site damage and durability (GRI-GG4), and pullout (ASTM D6706, GRI-GG5) and connection (ASTM D6638) test data.

1. Manufacturing Quality Control - The geosynthetic manufacturer shall have a quality control program that includes QC testing no less frequently than each 400,000 square feet of production. The testing, as a minimum, shall include tensile strength per ASTM D4595.

2. Acceptable geogrid reinforcement products: Tensar UXMSE structural Geogrid; Mirafi Miragrid XT geogrids; Huesker Fortrac Geogrids; Strata Stratagrid Geogrids; or approved equal.

2.3. DRAINAGE

A. The MSE wall drainage system shall be designed to account for tributary storm water runoff area.

B. There shall be a drainage swale at the top of each wall as depicted in the plans.

C. Drainage layer fill shall consist of clean 1-inch minus crushed rock or crushed gravel meeting the gradation per ASTM D422.

Sieve Size Percent Passing 1 inch 100 ¾ inch 75 – 100 No. 4 0 – 60 No. 40 0 – 50 No. 200 0 – 5

D. The drainage collection pipe shall be a perforated or slotted Schedule 80 PVC or

corrugated HDPE pipe. The pipe may be covered with a geotexile sock that will function as a filter. The drainage pipe shall be manufactured in accordance with ASTM Dl248 or ASTM D3043.

E. Geocomposite drainage layer can be used as an alternative to the drainage layer. Geocomposite drainage layer shall be manufactured specially for use as geosynthetic drainage composite in reinforced soil construction; and shall consist of a core drainge net with geotextile filter membranes bonded to both sides of the drainge net.

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Acceptable geocomposite drainage layer are Mirafi G200N G- Series Drainage Composite; Layfield double-sided geocomposite drainge layer (Geo-Net 6 core drainge net with LP8 nonwoven geotextile bonded on two sides); or equal.

F. Drainage system shall be designed as recommended for free draining backfill materials in section 5.3 FHWA (2009) manual, if the reinforced backfill is of the type “AASHTO/FHWA Mandated) materials defined in paragraph 2.4 below (percent passing No. 200 sieve: 0-15). Drainage detail shown on the plans (Sheet No. W3154) shall be used, if reinforced backfill is not free draining (i.e. contains more that 15% constituents passing No. 200 sieve). Additional drainage elements (e.g., collector ipe, drain tile, etc.) may be required in the non-free draining reinforced backfill. Alternatives for the drainage system shown on the plans may be used by the CONTRACTOR. A detailed layout of this equivalent drainage system shall be provided by the CONTRACTOR and approved by the Engineer.

2.4. REINFORCED BACKFILL

A. All fill material used in the structure volume for MSE wall structures should be reasonably free from organic or other deleterious materials and should conform to the gradation limits, PI and soundness criteria provided in FHWA guidelines listed below. The reinforced fill should be well-graded in accordance with the Unified Soil Classification System in ASTM D2487. Unstable broadly graded soils (i.e., Cu > 20 with concave upward grain size distributions) and gap graded soils should be avoided.

MSE Wall Select Granular Reinforced Fill Requirements

Gradation: (AASHTO T-27)

U.S. Sieve Size Percent Passing(a) 4 in. (102 mm) (a, b) 100 No. 40 (0.425 mm) 0-60 No. 200 (0.075 mm) 0-15

Plasticity Index, PI (AASHTO T-90)

PI < 6

Soundness: (AASHTO T-104)

The materials shall be substantially free of shale or other soft, poor durability particles. The material shall have a magnesium sulfate soundness loss of less than 30 percent after four cycles (or a sodium sulfate value less than 15 percent after five cycles).

Notes: (a) To apply default F* values, Cu, should be greater than or equal to 4. (b) As a result of recent research on construction survivability of geosynthetics and epoxy coated reinforcements, it is recommended that the maximum particle size for these materials be reduced to ¾-in. (19 mm) for geosynthetics, and epoxy and PVC coated steel reinforcements unless construction damage assessment tests are or have been performed on the reinforcement combination with the specific or similarly graded large size granular fill. Prequalification tests on reinforcements using standard agency fill materials should be considered. CONTRACTOR can perform construction damage assessment tests on the reinforcement combination with the specific or similarly graded granular material as described in this table. If the results indicate that the reinforcement combination is undamaged CONTRACTOR will be permitted to utilize material between 4 in. and ¾ in. size.

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B. It is recommended that the above FHWA select granular reinforced fill properties be used. However, if the available soil at site does not accommodate these properties, the following fill properties can be used for the soil within the reinforced backfill zone subject to the approval of the Engineer. 1. Less than 35% passing the standard No. 200 sieve per ASTM D422 with a

maximum size of 3/4 inches.

2. A plasticity index less than 20 per ASTM D4318, unless allowed by the Engineer.

3. An effective angle of internal friction per ASTM D3080 as specified in the MSE wall system design calculations and working drawings at the specified compaction.

4. Soil pH in the range of 3 to 9 per Caltrans CTM 643. Corrosivity of the soils for use as reinforced backfill, at a minimum as applicable, shall be evaluated or conform to FHWA Corrosion/Degradation of Soil Reinforcements for Mechanically Stabilized Earth Walls and Reinforced Soil Slopes, Caltrans Corrosion Guidelines, Caltrans CTM 417, and Caltrans CTM 422.

5. Less than 0.5% organic material.

6. Material generated from site-excavated soils where the above requirement can be met. Unsuitable soils for backfill including MH, CH or Pt per ASTM D2487 shall not be used in the reinforced backfill zone.

G. The use of an effective angle of internal friction greater than the values specified for reinforced backfill in Paragraph 1.4C (30 degrees) for design shall be verified by appropriate testing, including testing frequency (if different from that specified below), submitted to and approved by the Engineer prior to construction.

H. Test soil properties during initial source evaluation or if a change in source. Sample reinforced backfill material once every 2,000 cubic yards and test for gradation and pH. Sample reinforced backfill material once every 15,000 cubic yards and test for internal friction angle, organic content, and resistivity. A variation in testing frequency may be required if a variation in material gradation or composition is observed. Change in testing frequency is subject to Engineer approval.

2.5. MATERIALS FOR BASE LEVELING PAD

A. Base leveling pad shall be constructed of crushed rock or crushed gravel meeting the gradation criteria for drainage layer fill, or Class A concrete (Greenbook) at the CONTRACTOR's option.

PART 3 -- EXECUTION

3.1. GENERAL

A. Construction shall be in accordance with the approved working drawings. Construction shall also follow the guidelines in the FHWA Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines, and the AASHTO Standard Specifications for Highway Bridges. In the event of conflict between any requirements of the FHWA or AASHTO construction guidelines, the more stringent requirements shall apply. The MSE systems shall be constructed to support the roadway to the lines and grades of the alignment shown on the Drawings.

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B. Control of surface water shall be in accordance with the relevant project’s guidelines.

3.2. EXCAVATION

A. The CONTRACTOR shall excavate to the lines and grades shown on the approved excavation plans required in the drawings. Temporary excavations and/or support of excavation systems, if required, shall be in accordance with the approved excavation and support of excavation plans.

B. The CONTRACTOR shall excavate to the lines and grades as shown on the CONTRACT DOCUMENTS and the approved working drawings for placement of blanket and chimney drainage layer.

3.3. BASE LEVELlNG PAD

A. A minimum 6 inches thick layer of materials for base leveling pad shall be placed up to the grades and locations as shown on the approved working drawings.

B. If crushed rock or crushed gravel is used for the leveling pad materials, it shall be densified to provide a firm, level bearing pad on which to place the first course of wall facing units.

C. If a concrete leveling pad is used, it shall be cured a minimum of 12 hours before placement of first course of segmental concrete units.

3.4. WALL FACING UNITS AND SOIL REINFORCEMENT PLACEMENT

A. All materials shall be installed at the indicated elevations and orientations as shown in the wall details on the CONTRACT DOCUMENTS and approved working drawings, unless otherwise directed by the Engineer. The wall facing units and geogrid reinforcements shall be installed in accordance with the manufacturer's recommendations. The approved working drawings shall govern in any conflict between these two requirements.

B. Geogrid reinforcements not providing a minimum stiffness (flexural rigidity) of 30,000 mg-cm per ASTM D1388 or wider than 12 feet shall be staked at the corners and on 12-foot centers along the roll edges to prevent wrinkling or other distortion of the reinforcement during backfill placement.

C. Overlap of the geogrid in the design strength direction shall not be permitted. The design strength direction, or principal strength direction, is that length of geogrid reinforcement perpendicular to the wall face and shall consist of one continuous piece of geogrid material. Adjacent sections of reinforcement shall be butted in a manner to assure 100-percent coverage after placement.

D. Geogrid reinforcements shall be installed under tension. A nominal tension shall be applied to the geogrid reinforcements and maintained by staples or stakes until the geogrid reinforcements have been covered by at least 6 inches of fill.

E. Splice of geogrids is not allowed.

F. Broken, chipped, stained, or otherwise damaged wall facing units and geogrid reinforcements shall not be placed in the MSE wall system.

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3.5. REINFORCED SOIL PLACEMENT

A. Prior to placement of a layer of geogrid reinforcement, the receiving subgrade shall be compacted and scarified to a maximum depth of 2 inches in preparation of the next layer of fill. The scarified surface shall be made horizontal and approximately level prior to geogrid placement. The scarification and leveling process shall include filling of all cleat holes created by sheepfoot rollers, as applicable. The geogrid shall be placed directly on the scarified surface.

B. Fill materials shall not be dumped directly onto the geogrids from trucks.

C. Fill materials shall be placed from the middle of the geogrid layer towards the ends of the geogrid to maintain tautness of the geogrid. The fill materials that are to be used as reinforced backfill shall be placed in horizontal layers 8 inches thick, maximum, measured before compaction, or maximum 6 inches for hand compaction equipment.

D. The fill material shall be placed, spread, and compacted in such a manner that eliminates the development of wrinkles or movement of the geogrid reinforcements and the segmental concrete units.

E. The reinforced backfill shall be and moisture-conditioned to approximately 2 percent above the optimum moisture content and compacted to no less than 95 percent maximum dry density as determined in accordance with ASTM D1557.

F. Only hand-operated compaction equipment is allowed within 3 feet of the back of the segmental concrete units.

G. Tracked construction equipment shall not be operated directly on the geogrid reinforcements. A minimum backfill thickness of 6 inches, measured after compaction, is required prior to operation of tracked vehicles over the geogrid reinforcements. The CONTRACTOR shall keep the turning of the tracked vehicles to a minimum to prevent displacing the compacted reinforcement backfill and damaging or moving the geogrid reinforcement. If displacement of the compacted reinforcement backfill, or damage or movement of the geogrid reinforcement is observed, the CONTRACTOR shall remove and reconstruct the affected backfill and geogrid reinforcement at the direction of the ENGINEER and at no additional cost to the OWNER.

H. Rubber-tired equipment may pass directly over uncoated geogrid reinforcement and be operated in accordance with the manufacturer's recommendations. Rubber-tired equipment shall be operated at speeds less than 10 mph. Sudden braking and sharp turning shall be avoided.

I. A minimum compacted fill thickness of 6 inches shall be required prior to operation of rubber-tired equipment over coated geogrids or tracked equipment or sheep foot compactors over any geogrid. This minimum compacted fill thickness may be adjusted by the Engineer, depending upon the length of the compaction feet on the sheepfoot roller, as applicable.

J. At the end of each day's operation, the CONTRACTOR shall slope the last level of backfill away from the wall facing to direct runoff of rainwater and surface water away from the wall face. Furthermore, the CONTRACTOR shall not allow surface runoff from adjacent areas to enter the wall construction site.

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3.6. DRAINAGE FILL PLACEMENT

A. Drainage fill shall be placed to the minimum finished thickness and widths as shown on the Drawings and approved working drawings.

B. A minimum of 1 cubic foot of drainage fill shall be used for each square foot of wall face and shall be placed within the cores of the segmental concrete units, between and behind the MSE wall facing units and shall extend back from the face of the wall a minimum of 2 feet.

C. Drainage collection pipes shall be installed to maintain gravity flow of water outside of and away from the reinforced backfill zone.

D. The main drainage collection pipes, just behind the heel of the wall facing segmental concrete units and behind the heel of the reinforced backfill zone, shall be perforated or slotted Schedule 80 PVC or double-walled corrugated HDPE pipe, and be a minimum of 6 inches in diameter. The main drainage collection pipes shall be constructed in accordance with the guidelines in the FHWA Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines and the NCMA Design Manual for Segmental Retaining Walls, or the recommendations of the manufacturers of the wall facing, whichever is more stringent.

E. The secondary drainage collection pipes shall be sloped a minimum of 1 percent to provide gravity flow from the main drainage collection pipe behind the back of the reinforced backfill zone to the main drainage collection pipe behind the heel of the wall facing units. Drainage laterals shall be spaced at 50 feet, maximum along the face of the MSE wall system, shall be sloped a minimum 1 percent for gravity flow, and shall daylight to the slope area in front of the MSE wall systems at an elevation lower than the lowest point of the pipe within the drainage fill. The secondary drainage collection pipes and the drainage laterals shall be perforated or slotted Schedule 80 PVC or corrugated HDPE pipe, and shall be a minimum of 6 inches in diameter.

F. Geocomposite drainage layer can be used as an alternative for chimney drainage layer at the CONTRACTOR’s option. The geocomposites drainage layer shall provide continuous, 100 percent coverage behind the reinforced backfill zone (no gaps) and shall connect to drain to the main drainage collection pipe behind the heel of the reinforced backfill zone. The geocomposites drainage layer shall be transported, handled, stored, and installed in accordance with the manufacture’s guidelines. The chimney drainage layer shall be 70% of the height of the MSE wall system or maximum elevation of groundwater rise, whichever is greater.

3.7. FIELD QUALITY CONTROL ASSURANCE

A. Horizontal and vertical construction tolerances of the wall facing units shall be in accordance with the manufacturer's recommendations and the following minimum requirements:

1. Base leveling pad at any given elevation of the embedment depth shall be constructed with a vertical tolerance of 1/8 inch to the design elevation of the approved working drawings and with a vertical elevation differential not to exceed 1 inch over 100 feet.

2. The geogrid reinforcement shall be placed within 3 inches of the design elevation of the approved working drawings.

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3. The face of the MSE wall system at top of the wall shall not deviate more than 3 inches horizontally from the lines and grades as indicated on the Drawings.

4. Deviation from the vertical shall be within 11/2 inches for the construction of the traffic barriers.

5. The overall tolerance relative to the wall design vertically or batter shall not exceed 2 degrees of the design batter. Walls shall not have a negative inclination with respect to the design batter angle, i.e., the top of the wall rotates away from the MSE wall systems with respect to the bottom of the segmental concrete units.

6. Bulging shall be within 1 inch over 10 feet.

B. At the direction of the ENGINEER, the MSE wall supplier shall provide a qualified and experienced manufacturer's representative on site for up to 5 days to assist the CONTRACTOR regarding the proper wall construction. The MSE wall supplier representative shall be provided at no additional cost to the OWNER.

- END OF SECTION -

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city of manhattan beach department of public works

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