By Vincent Riley,2014-03-29 01:55
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    1.01 Description

    A. Work includes furnishing and installing segmental retaining wall (SRW) units to the lines and grades

    designated on the project’s final construction drawings or as directed by the Architect/Engineer. Also

    included is furnishing and installing appurtenant materials required for construction of the retaining wall

    as shown on the construction drawings.

    1.02 Reference Standards

A. Segmental Retaining Wall Units

    1. ASTM C 1372 - Standard Specification for Segmental Retaining Wall Units

    2. ASTM C 140 - Standard Test Methods of Sampling and Testing Concrete Masonry Units

B. Geosynthetic Reinforcement

    1. ASTM D 4595 - Tensile Properties of Geotextiles by the Wide-Width Strip Method

    2. ASTM D 5262 - Test Method for Evaluating the Unconfined Creep Behavior of


    3. GRI:GG1 - Single Rib Geogrid Tensile Strength

    4. GRI:GG5 - Geogrid Pullout

C. Soils

    1. ASTM D 698 - Moisture Density Relationship for Soils, Standard Method

    2. ASTM D 422 - Gradation of Soils

    3. ASTM D 424 - Atterberg Limits of Soil

D. Drainage Pipe

    1. ASTM D 3034 - Specification for Polyvinyl Chloride (PVC) Plastic Pipe

    2. ASTM D 1248 - Specification for Corrugated Plastic Pipe

E. Engineering Design

    1. “NCMA Design Manual for Segmental Retaining Walls”, Second Edition

    F. Where specifications and reference documents conflict, the Architect/Engineer shall make the final

    determination of applicable document.

    1.03 Submittals

    A. Material Submittals: The Contractor shall submit manufacturers' certifications two weeks prior to start

    of work stating that the SRW units and geosynthetic reinforcement meet the requirements of Section 2

    of this specification.

    B. Design Submittal: The Contractor shall submit two sets of detailed design calculations and final

    retaining wall plans for approval at least two weeks prior to the beginning of wall construction. All

    calculations and drawings shall be prepared and sealed by a professional Civil Engineer (P.E.) (Wall

    Design Engineer) experienced in SRW design and licensed in the state where the wall is to be built.

    1.04 Delivery, Storage and Handling

    A. Contractor shall check materials upon delivery to assure that specified type and grade of materials have

    been received and proper color and texture of SRW units have been received.

    B. Contractor shall prevent excessive mud, wet concrete, epoxies, and like materials that may affix

    themselves, from coming in contact with materials.

    C. Contractor shall store and handle materials in accordance with manufacturer's recommendations.

    D. Contractor shall protect materials from damage. Damaged materials shall not be incorporated into the

    retaining wall.


    2.01 Segmental Retaining Wall Units

    A. SRW units shall be machine formed, Portland Cement concrete blocks specifically designed for

    retaining wall applications. SRW units currently approved for this project are:

    VERSA-LOK Mosaic Retaining Wall System that includes three unit types: VERSA-LOK Standard

    units, VERSA-LOK Cobble units and VERSA-LOK Accent units, as manufactured by


B. Color of SRW units shall be _____________.

    C. Finish of SRW units shall be split face.

    D. SRW unit faces shall be of straight geometry.

    E. SRW unit heights shall be both four and six inches.

    F. SRW units shall be designed to stack in 10 inch high by 24 inch wide “panels” consisting of the three

    SRW unit types that can be stacked in varied patterns to create a random look.

    G. SRW units (not including aggregate fill in unit voids) shall provide a minimum weight of 105 psf wall

    face area.

    H. SRW units shall be solid through the full depth of the unit.

    I. SRW units shall have a depth (front face to rear) to height ratio of 2:1, minimum.

    J. SRW units shall be interlocked with connection pins, which provide ? inch setback from the unit below

    (four and six-inch high are stacked alternately, yielding an overall 8.5 degree cant from vertical). K. SRW units shall be capable of being erected with the horizontal gap between adjacent units not

    exceeding 1/8 inches.

    L. SRW units shall be capable being installed with a continuous, level course at every 10 inches of height

    so geosynthetic reinforcement layers can be placed level within the wall face.

    M. SRW units shall be capable of providing overlap of units on each successive course of a corner so that

    walls meeting at corner are interlocked and continuous. SRW units that require corners to be mitered

    shall not be allowed.

    N. SRW units shall be sound and free of cracks or other defects that would interfere with the proper

    placing of the unit or significantly impair the strength or permanence of the structure. Cracking or

    excessive chipping may be grounds for rejection. Units showing cracks longer than 1/2" shall not be

    used within the wall. Units showing chips visible at a distance of 30 feet from the wall shall not be used

    within the wall.

    O. Concrete used to manufacture SRW units shall have a minimum 28 days compressive strength of 3,000

    psi and a maximum moisture absorption rate, by weight, of 8% as determined in accordance with

    ASTM C140. Compressive strength test specimens shall conform to the saw-cut coupon provisions of

    ASTM C140.

    P. SRW units' molded dimensions shall not differ more than + 1/8 inch from that specified, in accordance

    with ASTM C1372.

    2.02 Segmental Retaining Wall Unit Connection Pins

    A. SRW units shall be interlocked with VERSA-Tuff Snap-Off connection pins, 6.8 inches in height, with a

    section which can snap-off, yielding a 4.6 inch high pin. The pins shall consist of glass-reinforced nylon

    made for the expressed use with the SRW units supplied.

    2.03 Geosynthetic Reinforcement

    A. Geosynthetic reinforcement shall consist of geogrids or geotextiles manufactured as a soil reinforcement

    element. The manufacturers/suppliers of the geosynthetic reinforcement shall have demonstrated

    construction of similar size and types of segmental retaining walls on previous projects.

    The geosynthetic type must be approved one week prior to bid opening. Geosynthetic types currently

    approved for this project are:

    VERSA-Grid Geogrids

    B. The type, strength, and placement location of the reinforcing geosynthetic shall be as determined by the

    Wall Design Engineer, as shown on the final, P.E. sealed retaining wall plans.

    2.04 Leveling Pad

    A. Material for leveling pad shall consist of compacted sand, gravel, or combination thereof (USCS soil

    types GP,GW, SP, & SW) and shall be a minimum of 6 inches in depth. Lean concrete with a strength

    of 200-300 psi and three inches thick maximum may also be used as a leveling pad material. The

    leveling pad should extend laterally at least a distance of 6 inches from the toe and heel of the

    lowermost SRW unit.

    2.05 Drainage Aggregate

    A. Drainage aggregate shall be angular, clean stone or granular fill meeting the following gradation as

    determined in accordance with ASTM D422

    Sieve Size Percent Passing

    1 inch 100

    3/4 inch 75-100

    No. 4 0-60

    No. 40 0-50

    No. 200 0-5

    2.06 Drainage Pipe

    A. The drainage collection pipe shall be a perforated or slotted PVC, or corrugated HDPE pipe. The

    drainage pipe may be wrapped with a geotextile to function as a filter.

    B. Drainage pipe shall be manufactured in accordance with ASTM D 3034 and/or ASTM D 1248

    2.07 Reinforced (Infill) Soil

    A. The reinforced soil material shall be free of debris. Unless otherwise noted on the final, P.E. sealed,

    retaining wall plans prepared by the Wall Design Engineer, the reinforced material shall consist of the

    inorganic USCS soil types GP, GW, SW, SP, SM, meeting the following gradation, as determined in

    accordance with ASTM D422:

    Sieve Size Percent Passing

    4 inch 100

    No. 4 20-100

    No. 40 0-60

    No. 200 0-35

    B. The maximum particle size of poorly-graded gravels (GP) (no fines) should not exceed 3/4 inch unless

    expressly approved by the Wall Design Engineer and the long-term design strength (LTDS) of the

    geosynthetic is reduced to account for additional installation damage from particles larger than this


C. The plasticity of the fine fraction shall be less than 20.


    3.01 Soil

    A. The following soil parameters, as determined by the Owner's Geotechnical Engineer shall be used for

    the preparation of the final design:

     Unit Weight Internal Friction Cohesion (c)

     () (pcf) Angle (;) (degrees)

    Reinforced Fill ________ ____________ 0

    Retained Soil ________ ____________ 0

    Foundation Soil ________ ____________ __________

    (If internal friction angles are not available for the above section, the

    specifier can provide the USCS soil type classification for the reinforced,

    retained, and foundation soils and/or attach the geotechnical investigation

    report for this project.)

    B. Should the actual soil conditions observed during construction differ from those assumed for the design,

    design shall be reviewed by the Wall Design Engineer at the Owner's Geotechnical Engineer's direction.

    3.02 Design

    A. The design analysis for the final, P.E. sealed retaining wall plans prepared by the Wall Design Engineer

    shall consider the external stability against sliding and overturning, internal stability, and facial stability

    of the reinforced soil mass and shall be in accordance with acceptable engineering practice and these

    specifications. The internal and external stability analysis shall be performed in accordance with the

    “NCMA Design Manual for Segmental Retaining Walls”, using the recommended minimum factors of

    safety in this manual.

    B. External stability analysis for bearing capacity, global stability, and total and differential settlement

    shall be the responsibility of the Owner and the Owner's Geotechnical Engineer. Geotechnical Engineer

    shall perform bearing capacity, settlement estimates, and global stability analysis based on the final wall

    design provided by the Wall Design Engineer and coordinate any required changes with Wall Design


    C. While vertical spacing between geogrid layers may vary, it shall not exceed 20 inches maximum in the

    wall design.

    D. The geosynthetic placement in the wall design shall have 100 percent continuous coverage parallel to

    the wall face. Gapping between horizontally adjacent layers of geosynthetic (partial coverage) will not

    be allowed.


    4.01 Inspection

    A. The Owner or Owner's Representative is responsible for verifying that the contractor meets all the

    requirements of the specification. This includes all submittals for materials and design, qualifications,

    and proper installation of wall system.

    B. Contractor's field construction supervisor shall have demonstrated experience and be qualified to direct

    all work at the site.

    4.02 Excavation

A. Contractor shall excavate to the lines and grades shown on the project grading plans. Contractor shall

    take precautions to minimize over-excavation. Over-excavation shall be filled with compacted infill

    material, or as directed by the Engineer/Architect, at the Contractor's expense.

    B. Contractor shall verify location of existing structures and utilities prior to excavation. Contractor shall

    ensure all surrounding structures are protected from the effects of wall excavation. Excavation support,

    if required, is the responsibility of the Contractor.

    4.03 Foundation Preparation

    A. Following the excavation, the foundation soil shall be examined by the Owner's Engineer to assure

    actual foundation soil strength meets or exceeds the assumed design bearing strength. Soils not meeting

    the required strength shall be removed and replaced with infill soils, as directed by the Owner's


    B. Foundation soil shall be proofrolled and compacted to 95% standard Proctor density and inspected by

    the Owner's Engineer prior to placement of leveling pad materials.

    4.04 Leveling Pad Construction

    A. Leveling pad shall be placed as shown on the final, P.E. sealed retaining wall plans with a minimum

    thickness of 6 inches. The leveling pad should extend laterally at least a distance of 6 inches from the

    toe and heel of the lower most SRW unit.

    B. Granular leveling pad material shall be compacted to provide a firm, level bearing surface on which to

    place the first course of units. Well-graded sand can be used to smooth the top 1/2 to 1/4 inch of the

    leveling pad. Compaction will be with mechanical plate compactors to achieve 95% of maximum

    standard Proctor density (ASTM D 698).

    4.05 SRW Unit Installation

    A. All SRW units shall be installed at the proper elevation and orientation as shown on the final, P.E.

    sealed wall plans and details on the construction plans or as directed by the Wall Design Engineer. The

    SRW units shall be installed in general accordance with the manufacturer's recommendations. The

    specifications and drawings shall govern in any conflict between the two requirements.

    B. For ease of installation, generally the base course of SRW units shall be all six-inch-high Standard units

    placed on the leveling pad. The units shall be leveled side-to-side, front-to-rear and with adjacent units,

    and aligned to ensure intimate contact with the leveling pad. The base course is the most important to

    ensure accurate and acceptable results. No gaps shall be left between the front of adjacent units.

    Alignment may be done by means of a string line or offset from base line to the back of the units.

    Placing panels of Mosaic directly on the leveling pad is also acceptable. In this case, the entire 10-inch-

    high course of panels must be installed before the level and alignment can be checked.

C. All excess debris shall be cleaned from top of units.

    D. Mosaic panels shall be placed on the units below. Each panel shall be installed completely prior to

    installing horizontally adjacent panels. Each Mosaic panel shall be 10 inches high by 24 inches wide,

    consisting of one Standard unit, one Cobble unit, and two Accent units. With each adjacent panel, the

    units at the bottom of the panels should be alternated from four-inch-high units to six-inch-high units.

    As an example, one panel shall have Accent units at the base of the panel with Standard and Cobble

    units on top. The next adjacent panel shall have the Standard and Cobble units at the bottom and

    Accent units on top. The order of the Cobble and Standard units shall be randomly mixed within the

    panels to avoid a repetitive pattern. The entire length of each 10-inch-high course of panels shall be

    installed before starting the next course of panels.

    E. Each unit in a Mosaic panel shall be pinned to the units below in the following manner: Two VERSA-

    Tuff connection pins shall be inserted through the pin holes of each unit into receiving slots in units

    below, creating an approximate ? inch setback from the unit below. Pins shall be fully seated in the pin

    slot below. When pinning four-inch-high Accent units, the top 2 inches of the 6.8 inch high pin will

    initially extend above the Accent unit. The top of the pin shall be snapped-off by hitting the top of the

    pin from the side. Once pinned, the units shall be pushed forward to remove any looseness in the unit-

    to-unit connection.

    F. Prior to placement of next course of panels, the level and alignment of the units shall be checked and

    corrected, where needed.

    G. The next course of panels shall be placed so that it is staggered at least four inches from the vertical

    joints between the panels below. The patterns in the Mosaic panels generally shall not line up with the

    course below. The bond of the panels shall be varied on subsequent courses to create a random look.

    H. Layout of curves and corners shall be installed in accordance with the wall plan details or in general

    accordance with SRW manufacturer's installation guidelines. Walls meeting at corners shall be

    interlocked by overlapping successive courses of panels. Special corner panels shall be installed such

    that both sides of the corner panels vertically align the upper and lower units to create 10-inch-high

    joints to butt against adjacent regular Mosaic panels. For each course of panels, the corner panels shall

    be installed first, then regular panels installed out from the corners.

    I. Procedures C. through G. shall be repeated until reaching top of wall units, just below the height of the

    cap units. Geosynthetic reinforcement, drainage materials, and reinforced backfill shall be placed in

    sequence with unit installation as described in Section 4.06, 4.07, and 4.08.

    4.06 Geosynthetic Reinforcement Placement

A. All geosynthetic reinforcement shall be installed at the proper elevation and orientation as shown on the

    final, P.E. sealed retaining wall plan profiles and details or as directed by the Wall Design Engineer.

    B. At the elevations shown on the final plans, (after the units, drainage material, and backfill have been

    placed to this elevation) the geosynthetic reinforcement shall be laid horizontally on compacted infill

    and on top of the concrete SRW units, to within one inch of the front face of the unit below.

    Embedment of the geosynthetic in the SRW units shall be consistent with SRW manufacturer's

    recommendations. Correct orientation of the geosynthetic reinforcement shall be verified by the

    Contractor to be in accordance with the geosynthetic manufacturer's recommendations. The highest

    strength direction of the geosynthetic must be perpendicular to the wall face.

    C. Geosynthetic reinforcement layers shall be one continuous piece for their entire embedment length.

    Splicing of the geosynthetic in the design strength direction (perpendicular to the wall face) shall not be

    permitted. Along the length of the wall, horizontally adjacent sections of geosynthetic reinforcement

    shall be butted in a manner to assure 100 percent coverage parallel to the wall face.

    D. Tracked construction equipment shall not be operated directly on the geosynthetic reinforcement. A

    minimum of 6 inches of backfill is required prior to operation of tracked vehicles over the geosynthetic.

    Turning should be kept to a minimum. Rubber-tired equipment may pass over the geosynthetic

    reinforcement at slow speeds (less than 5 mph).

    E. The geosynthetic reinforcement shall be free of wrinkles prior to placement of soil fill. The nominal

    tension shall be applied to the reinforcement and secured in place with staples, stakes, or by hand

    tensioning until reinforcement is covered by six inches of fill.

    4.07 Drainage Materials

    A. Drainage aggregate shall be installed to the line, grades, and sections shown on the final P.E. sealed

    retaining wall plans. Drainage aggregate shall be placed to the minimum thickness shown on the

    construction plans between and behind units (a minimum of one cubic foot for each exposed square foot

    of wall face unless otherwise noted on the final wall plans).

    B. Drainage collection pipes shall be installed to maintain gravity flow of water outside the reinforced soil

    zone. The drainage collection pipe shall daylight into a storm sewer or along a slope, at an elevation

    lower than the lowest point of the pipe within the aggregate drain.

    4.08 Backfill Placement

    A. The reinforced backfill shall be placed as shown in the final wall plans in the maximum compacted lift

    thickness of 10 inches and shall be compacted to a minimum of 95% of standard Proctor density

    (ASTM D 698) at a moisture content within 2% of optimum. The backfill shall be placed and spread in

    such a manner as to eliminate wrinkles or movement of the geosynthetic reinforcement and the SRW


    B. Only hand-operated compaction equipment shall be allowed within 3 feet of the back of the wall units.

    Compaction within the 3 feet behind the wall units shall be achieved by at least three (3) passes of a

    lightweight mechanical tamper, plate, or roller.

    C. At the end of each day's operation, the Contractor shall slope the last level of backfill away from the

    wall facing and reinforced backfill to direct water runoff away from the wall face.

    D. At completion of wall construction, backfill shall be placed level with final top of wall elevation. If final

    grading, paving, landscaping, and/or storm drainage installation adjacent to the wall is not placed

    immediately after wall completion, temporary grading and drainage shall be provided to ensure water

    runoff is not directed at the wall nor allowed to collect or pond behind the wall until final construction

    adjacent to the wall is completed.

    4.09 SRW Caps

    A. SRW caps shall be properly aligned and glued to underlying units with VERSA-LOK adhesive, a

    flexible, high-strength concrete adhesive. Rigid adhesive or mortar are not acceptable.

    B. Caps shall overhang the top course of units by 3/4 to 1 inch. Slight variation in overhang is allowed to

    correct alignment at the top of the wall.

    4.10 Construction Adjacent to Completed Wall

    A. The Owner or Owner's Representative is responsible for ensuring that construction by others adjacent to

    the wall does not disturb the wall or place temporary construction loads on the wall that exceed design

    loads, including loads such as water pressure, temporary grades, or equipment loading. Heavy paving

    or grading equipment shall be kept a minimum of three feet behind the back of the wall face.

    Equipment with wheel loads in excess of 150 psf live load shall not be operated within 10 feet of the

    face of the retaining wall during construction adjacent to the wall. Care should be taken by the General

    Contractor to ensure water runoff is directed away from the wall structure until final grading and surface

    drainage collection systems are completed.


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