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| Section 2834 MODULAR CONCRETE RETAINING WALL PART 1: GENERAL 1.01 Description A. Work shall consist of furnishing and construction of a KEYSTONE Retaining Wall System or equal in accordance with these specifications and in reasonably close conformity with the lines, grades, design, and dimensions shown on the plans. B. Work includes preparing foundation soil, furnishing and installing leveling pad, unit drainage fill and backfill to the lines and grades shown on the construction drawings. C. Work includes furnishing and installing geogrid soil reinforcement of the type, size, location, and lengths designated on the construction drawings. 1.02 Related Sections A. Section 02100 - Site Preparation B. Section 02200 - Earthwork 1.03 Reference Documents A. American Society for Testing and Materials (ASTM) 1. ASTM C-1372 Specification for Segmental Retaining Wall Units 2. ASTM D-422 Particle Size Analysis 3. ASTM D-698 Laboratory Compaction Characteristics of Soil -Standard Effort 4. ASTM D-4318 Liquid Limit, Plastic Limit and Plasticity Index of Soils 5. ASTM D-4595 Tensile Properties of Geotextiles - Wide Width Strip 6. ASTM D-5262 Unconfined Tension Creep Behavior of Geosynthetics 7. ASTM D-3034 Polyvinyl Chloride Pipe (PVC) 8. ASTM D-1248 Corrugated Plastic Pipe B. Geosynthetic Research Institute (GRI) 1. GRI-GG4 Determination of Long Tern Design Strength of Geogrids 2. GRI-GG5 Determination of Geogrid (soil) Pullout C. National Concrete Masonry Association (NCMA) 1. NCMA SRWU-1 Test Method for Determining Connection Strength of SRW 2. NCMA SRWU-2 Test Method for Determining Shear Strength of SRW 1.04 Submittals/Certification A. Contractor shall submit a Manufacturer's certification, prior to start of work, that the retaining wall system components meet the requirements of this specification and the structure design. B. Contractor shall submit construction drawings and design calculations for the retaining wall system prepared and stamped by a Professional Engineer registered in the state of the project. The engineering designs, techniques, and material evaluations shall be in accordance with the KEYSTONE Design Manual, NCMA Design Guidelines For Segmental Retaining Walls, or the AASHTO Standard Specifications for Highway Bridges, Section 5.8 (whichever is applicable to designer). C. Contractor shall submit a test report documenting strength of specific modular concrete unit and geogrid reinforcement connection. The maximum design tensile load of the geogrid shall be equal to the laboratory tested ultimate strength of geogrid / facing unit connection at a maximum normal force limited by the "Hinge Height" of the structure divided by a safety factor of 1.5. The connection strength evaluation shall be performed in accordance with NCMA test method SRWU-1. 1.05 Quality Assurance A. Contractor shall submit certification, prior to start of work, that the retaining wall system (modular concrete units and specific geogrid): 1) has been successfully utilized on a minimum of five (5) similar projects, i.e., height, soil fill types, erection tolerances, etc.; and 2) has been successfully installed on a minimum of 1 million (1,000,000) square feet of retaining walls. B. Contractor shall submit a list of five (5) previously constructed projects of similar size and magnitude by the wall installer where the specific retaining wall system has been constructed successfully. Contact names and telephone numbers shall be listed for each project. C. Contractor shall provide evidence that the design engineer has a minimum of five years of documentable experience in the design for reinforced soil structures. The design engineer shall provide proof of current professional liability insurance with an aggregate coverage limit of not less than $2,000,000. D. Owner shall provide soil testing and quality assurance inspection during earthwork and wall construction operations. Owner's quality assurance program does not relieve the contractor of responsibility for wall performance. 1.06 Delivery, Storage and Handling A. Contractor shall check all materials upon delivery to assure that the proper type, grade, color, and certification has been received. B. Contractor shall protect all materials from damage due to jobsite conditions and in accordance with manufacturer's recommendations. Damaged materials shall not be incorporated into the work. PART 2: PRODUCTS 2.01 Definitions A. Modular Unit - a concrete retaining wall element machine made from portland cement, water, and aggregates. B. Structural Geogrid - a structural element formed by a regular network of integrally connected tensile elements with apertures of sufficient size to allow interlocking with surrounding soil, rock, or earth and function primarily as reinforcement. C. Unit Drainage Fill - drainage aggregate which is placed within and immediately behind the modular concrete units. D. Reinforced Backfill - compacted soil which is placed within the reinforced soil volume as outlined on the plans. 2.02 Modular Concrete Retaining Wall Units A. Modular concrete units shall conform to the following architectural requirements: face color - concrete gray - standard manufacturers' color may be specified by the Owner. face finish - sculptured rock face in angular tri-planer configuration. Other face finishes will not be allowed without written approval of Owner. bond configuration - running with bonds nominally located at midpoint vertically adjacent units, in both straight and curved alignments. exposed surfaces of units shall be free of chips, cracks or other imperfections when viewed from a distance of 10 feet under diffused lighting. B. Modular concrete materials shall conform to the requirements of ASTM C1372 - Standard Specifications for Segmental Retaining Wall Units. C. Modular concrete units shall conform to the following structural and geometric requirements measured in accordance with appropriate references: compressive strength = 3000 psi minimum; absorption = 8 % maximum (6% in northern states) for standard weight aggregates; dimensional tolerances = ± 1/8" from nominal unit dimensions not including rough split face, ±1/16" unit height - top and bottom planes; unit size - 8" (H) x 18" (W) x 18" (D) minimum; unit weight - 100 lbs/unit minimum for standard weight aggregates; inter-unit shear strength - 1500 plf minimum at 2 psi normal pressure; geogrid/unit peak connection strength -1000 plf minimum at 2 psi normal force. D. Modular concrete units shall conform to the following constructability requirements: vertical setback = 1/8"± per course (near vertical) or 1"+ per course per the design; alignment and grid positioning mechanism - fiberglass pins, two per unit minimum; maximum horizontal gap between erected units shall be - 1/2 inch. 2.03 Shear Connectors A. Shear connectors shall be 1/2 inch diameter thermoset isopthalic polyester resin-pultruded fiberglass reinforcement rods or equivalent to provide connection between vertically and horizontally adjacent units. Strength of shear connectors between vertical adjacent units shall be applicable over a design temperature of 10 degrees F to + 100 degrees F. B. Shear connectors shall be capable of holding the geogrid in the proper design position during grid pre-tensioning and backfilling. 2.04 Base Leveling Pad Material A. Material shall consist of a compacted crushed stone base or non-reinforced concrete as shown on the construction drawings. 2.05 Unit Drainage Fill A. Unit drainage fill shall consist of clean 1" minus crushed stone or crushed gravel meeting the following gradation tested in accordance with ASTM D-422: Sieve Size Percent Passing 1 inch 100 3/4 inch 75-100 No. 4 0 - 10 No. 50 0 - 5 B. One cubic foot, minimum, of drainage fill shall be used for each square foot of wall face. Drainage fill shall be placed within cores of, between, and behind units to meet this requirement. 2.06 Reinforced Backfill A. Reinforced backfill shall be free of debris and meet the following gradation tested in accordance with ASTM D-422: Sieve Size Percent Passing 2 inch 100-75 3/4 inch 100-75 No. 40 0-60 No. 200 0-35 Plasticity Index (PI) <15 and Liquid Limit <40 per ASTM D-4318. B. The maximum aggregate size shall be limited to 3/4 inch unless field tests have been performed to evaluate potential strength reductions to the geogrid design due to damage during construction. C. Material can be site excavated soils where the above requirements can be met. Unsuitable soils for backfill (high plastic clays or organic soils) shall not be used in the backfill or in the reinforced soil mass. D. Contractor shall submit reinforced fill sample and laboratory test results to the Architect/Engineer for approval prior to the use of any proposed reinforced fill material. 2.07 Geogrid Soil Reinforcement A. Geosynthetic reinforcement shall consist of geogrids manufactured specifically for soil reinforcement applications and shall be manufactured from high tenacity polyester yarn or high density polyethylene. Polyester geogrid shall be knitted from high tenacity polyester filament yarn with a molecular weight exceeding 25,000 Meg/m and a carboxyl end group values less than 30. Polyester geogrid shall be coated with an impregnated PVC coating that resists peeling, cracking, and stripping. B. Ta, Long Term Allowable Tensile Design Load, of the geogrid material shall be determined as follows: Ta = Tult / (RFcr*RFd*RFid*FS) Ta shall be evaluated based on a 75 year design life. 1. Tult, Short Term Ultimate Tensile Strength Tult is based on the minimum average roll values (MARV) 2. RFcr, Reduction Factor for Long Term Tension Creep RFcr shall be determined from 10,000 hour creep testing performed in accordance with ASTM D5262. Reduction value = 1.60 minimum. 3. RFd, Reduction Factor for Durability RFd shall be determined from polymer specific durability testing covering the range of expected soil environments. RFd = 1.10 minimum. 4. RFid, Reduction Factor for Installation Damage RFid shall be determined from product specific construction damage testing performed in accordance with GRI-GG4. Test results shall be provided for each product to be used with project specific or more severe soil type. RFid = 1.10 minimum. 5. FS, Overall Design Factor of Safety FS shall be 1.5 unless otherwise noted for the maximum allowable working stress calculation. C. The maximum design tensile load of the geogrid shall not exceed the laboratory tested ultimate strength of the geogrid/facing unit connection as limited by the "Hinge Height" divided by a factor of safety of 1.5. The connection strength testing and computation procedures shall be in accordance with NCMA SRWU-1 Test Method for Determining Connection Strength of SRW. D. Soil Interaction Coefficient, Ci Ci values shall be determined per GRI:GG5 at a maximum 0.75 inch displacement. E. Manufacturing Quality Control The geogrid manufacturer shall have a manufacturing quality control program that includes QC testing by an independent laboratory. The QC testing shall include: Tensile Strength Testing Melt Flow Index (HDPE) Molecular Weight (Polyester) 2.08 Drainage Pipe A. If required, the drainage pipe shall be perforated or slotted PVC pipe manufactured in accordance with ASTM D-3034 or corrugated HDPE pipe manufactured in accordance with ASTM D-1248. PART 3 EXECUTION 3.01 Excavation A. Contractor shall excavate to the lines and grades shown on the construction drawings. Owner's representative shall inspect the excavation and approve prior to placement of leveling material or fill soils. Proof roll foundation area as directed to determine if remedial work is required. B. Over-excavation and replacement of unsuitable foundation soils and replacement with approved compacted fill will be compensated as agreed upon with the Owner. 3.02 Base Leveling Pad A. Leveling pad material shall be placed to the lines and grades shown on the construction drawings, to a minimum thickness of 6 inches and extend laterally a minimum of 6" in front and behind the modular wall unit. B. Soil leveling pad materials shall be compacted to a minimum of 95 % Standard Proctor density per ASTM D-698 C. Leveling pad shall be prepared to insure full contact to the base surface of the concrete units. 3.03 Modular Unit Installation A. First course of units shall be placed on the leveling pad at the appropriate line and grade. Alignment and level shall be checked in all directions and insure that all units are in full contact with the base and properly seated. B. Place the front of units side-by-side. Do not leave gaps between adjacent units. Layout of corners and curves shall be in accordance with manufacturer's recommendations. C. Install shear/connecting devices per manufacturer's recommendations. D. Place and compact drainage fill within and behind wall units. Place and compact backfill soil behind drainage fill. Follow wall erection and drainage fill closely with structure backfill. E. Maximum stacked vertical height of wall units, prior to unit drainage fill and backfill placement and compaction, shall not exceed two courses. 3.04 Structural Geogrid Installation A. Geogrid shall be oriented with the highest strength axis perpendicular to the wall alignment. B. Geogrid reinforcement shall be placed at the strengths, lengths, and elevations shown on the construction design drawings or as directed by the Engineer. C. The geogrid shall be laid horizontally on compacted backfill and attached to the modular wall units. Place the next course of modular concrete units over the geogrid. The geogrid shall be pulled taut, and anchored prior to backfill placement on the geogrid. D. Geogrid reinforcements shall be continuous throughout their embedment lengths and placed side-by-side to provide 100% coverage at each level. Spliced connections between shorter pieces of geogrid or gaps between adjacent pieces of geogrid are not permitted. 3.05 Reinforced Backfill Placement A. Reinforced backfill shall be placed, spread, and compacted in such a manner that minimizes the development of slack in the geogrid and installation damage. B. Reinforced backfill shall be placed and compacted in lifts not to exceed 6 inches where hand compaction is used, or 8 - 10 inches where heavy compaction equipment is used. Lift thickness shall be decreased to achieve the required density as required. C. Reinforced backfill shall be compacted to 95% of the maximum density as determined by ASTM D698. The moisture content of the backfill material prior to and during compaction shall be uniformly distributed throughout each layer and shall be dry of optimum, + 0%, - 3%. D. Only lightweight hand-operated equipment shall be allowed within 3 feet from the tail of the modular concrete unit. E. Tracked construction equipment shall not be operated directly upon the geogrid reinforcement. A minimum fill thickness of 6 inches is required prior to operation of tracked vehicles over the geogrid. Tracked vehicle turning should be kept to a minimum to prevent tracks from displacing the fill and damaging the geogrid. F. Rubber tired equipment may pass over geogrid reinforcement at slow speeds, less than 10 MPH. Sudden braking and sharp turning shall be avoided. G. At the end of each day's operation, the Contractor shall slope the last lift of reinforced backfill away from the wall units to direct runoff away from wall face. The Contractor shall not allow surface runoff from adjacent areas to enter the wall construction site. 3.06 Cap Installation A. Cap units shall be glued to underlying units with an all-weather adhesive recommended by the manufacturer. 3.07 As-built Construction Tolerances A. Vertical alignment : ± 1.5" over any 10' distance. B. Wall Batter: within 2 degrees of design batter. C. Horizontal alignment: ± 1.5" over any 10' distance. Corners, bends, curves ± 1 ft to theoretical location. D. Maximum horizontal gap between erected units shall be 1/2 inch. 3.08 Field Quality Control A. The Owner shall engage inspection and testing services, including independent laboratories, to provide quality assurance and testing services during construction. This does not relieve the Contractor from securing the necessary construction control testing during construction. B. Testing and inspections services shall only be performed by qualified and experienced technicians and engineers. C. As a minimum, quality assurance testing should include foundation soil inspection, soil and backfill testing, verification of design parameters, and observation of construction for general compliance with design drawings and specifications. PART 4 MEASUREMENT AND PAYMENT |
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