CONCRETE SEGMENTAL RETAINING WALLS

Transcription

1 CONCRETE SEGMENTAL RETAINING WALLS 1.00 GENERAL 1.01 DESCRIPTION A. The work shall consist of furnishing and installing concrete segmental retaining wall (CSRW) units to the lines, grades and dimensions shown on the detailed drawinsg and as specified herein. B. Work includes furnishing leveling pad, unit fill and backfill material as specified herein and as shown on the construction shop drawings. C. Work includes furnishing approved CSRW facing and cap units as shown on the construction shop drawings. D. Work includes installation of wall drainage system as shown on the construction shop drawings. E. Work includes furnishing soil reinforcement as shown on the construction shop drawings DEFINITIONS A. Concrete Segmental Retaining Wall Facing (CSRW) Units: a preapproved facing unit which meets all physical and performance criteria in this specification, as determined by the ENGINEER prior to award of the contract, machine made from Portland Cement, water and mineral aggregates. B. CSRW Cap Unit: a unit designed specifically to top or finish an approved CSRW Unit. C. Unit Fill: aggregate fill placed in the open areas of CSRW units. D. Foundation Soil: compacted or in-situ soil beneath the entire wall. E. Soil Reinforcement Geogrid: a structural geotextile 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 structural reinforcement, as specified in Division 31 Section GEOGRID SOIL REPLACEMENT. F. Reinforced Backfill: compacted soil which is reinforced with geogrid, as defined by the reinforced soil volume indicated on the plans. G. Retained Soil: compacted or in-situ soil behind the reinforced backfill zone. H. Leveling Pad: a level compacted gravel or unreinforced concrete footing upon which the first course of CSRW units are placed REFERENCE DOCUMENTS A. Geosynthetic Research Institute GG1-87 Standard Test Method for Geogrid Rib Tensile Strength GG2-87 Standard Test Method for Geogrid Junction Strength GG3 (a&b)-91 Tension Creep Testing of (Stiff & Flexible) Geogrids GG4 (a&b)-91 Determination of Long-Term Design Strength of (Stiff & Flexible) Geogrids Concrete Segmental Retaining Wall

2 GG5-91 Geogrid Pullout B. American Society for Testing and Materials Standards ASTM CB-90 Specification for Concrete Aggregates ASTM C Hollow Load-Bearing Masonry Units ASTM C Methods of Sampling and Testing Concrete Masonry Units ASTM C Solid Load Bearing Concrete Masonry Units ASTM C Specification for Portland Cement ASTM C Specification for Blended Hydraulic Cements ASTM D-698 Moisture Density Relationship for Soils, Standard Method ASTM D-1557 Modified Proctor Density ASTM D-422 Gradation Analysis ASTM D-4318 Atterberg Limits ASTM D-4595 Tensile Properties of Geotextiles by the Wide-Width Strip Method ASTM D-4632 Tensile Properties of Geotextiles ASTM D-52 Tensile Creep Testing of Geosynthetics ASTM G Resistivity ASTM G Alkalinity C. NCMA TEK 50 A Specifications for Segmental Retaining Wall Units D. NCMA SRWU-1 Determination of Connection Strength between E. Geosynthetics and Segmental Concrete Units F. NCMA SRWU-2 Determination of Shear Strength between Segmental G. Concrete Units H. NCMA Design Manual for Segmental Retaining Wall 1.04 SUBMITTALS Submittals shall be in accordance with Division 1 Section SUBMITTALS PROCEDURES, and shall include: A. A minimum of the previous two years experience and a minimum of 40,000 square feet of documentable satisfactory experience installing Soil Reinforced Segmental Retaining Walls over eight feet in height. Provide a project list indicating the required experience before beginning construction of CSRW walls. B. Manufacturer s specifications (latest edition) for proposed materials, method of installation, and list of materials proposed for use. C. Samples of CSRW units showing finish and potential color variation shall be provided to the OWNER prior to construction. D. A notarized manufacturer s certification prior to start of work stating the CSRW system meets the requirements of this specification. E. A certificate of compliance with test report documentation certifying that the reinforced backfill materials comply with Section 2.03 of this specification. F. Detailed CSRW shop drawings, sealed by a Professional Engineer licensed in the state where the wall is to be constructed, including: Concrete Segmental Retaining Wall

3 1. Proprietary product literature indicating specifically which CSRW units are proposed for use on the project, including color, face style, and texture. 2. Proprietary product specifications indicating compressive strength, unit weight, aggregate mix, and percent absorption for the units proposed. 3. Proprietary product literature for soil reinforcements proposed for use in the CSRW system indicating exactly which reinforcements are to be used, wide width tensile strength, and results of 10,000 hour testing. This information should also include manufacturer recommended reduction factors for creep, biological/chemical damage, installation damage, factor of safety for uncertainties, and any other reductions identified by the manufacturer to be used for design with the proposed reinforcement. 4. Results of connection strength testing performed by a certified testing laboratory for the specific CSRW unit and specific soil reinforcements proposed according to NCMA test method SRWU Results of shear strength testing between CSRW units performed by a certified testing laboratory according to NCMA test method SRWU Wall profiles, reinforcement elevations, reinforcement lengths, reinforcement types, top of wall, bottom of wall, proposed grades at top of wall, and stations showing beginning of and ending of wall as well as the beginning and ending of turns and radii. 7. Design parameters for the retaining wall, including the design criteria specified herein, required bearing capacity of wall subgrade, and construction details. 8. Hand calculations and/or computer output accompanied by hand calculations addressing required design parameters according to NCMA recommendations. 9. A certificate of Errors and Omissions Insurance with a minimum value of $500,000 per occurrence for the Licensed Professional Engineer sealing the shop drawings DELIVERY, STORAGE AND HANDLING A. Check the materials upon delivery to assure the specified type, grade, color and texture of CSRW units have been received. B. Prevent excessive mud, wet concrete, epoxies, and like materials which may affix themselves, from coming in contact with the materials. C. Protect the materials from damage. Damaged material shall not be incorporated into the retaining wall structure SPECIAL PROVISIONS A. Unless otherwise shown on the plans, wall batter shall be a maximum of 4 degrees. Blocks shall be placed horizontally, and positive means of obtaining batter shall be provided. B. The Contractor s Professional Engineer responsible for design of the CSRW wall shall interpret subsurface conditions within the CSRW foundation area, and shall provide recommendations for any subsoil improvements required. Foundation area of concrete segmental retaining walls shall be taken to extend from a minimum of 6 inches from the front face of the block to the horizontal extent of the geogrid reinforcement. C. Include the cost of all means of subsoil improvement as recommended by the Contractor s Professional Engineer in the unit price bid per SF of facing area. D. Prior to undertaking any grading or excavation of the site, survey to confirm the location of the retaining walls, as well as any underground features, including utility locations within the area of construction. Concrete Segmental Retaining Wall

4 E. Coordinate installation of underground utilities with wall installation. F. Minimum geogrid length shall be five feet or 70 percent of the wall height, whichever is greater. G. The Design Criteria for the CSRW system shall be: 2.00 MATERIALS 1. Internal Stability of Walls: Minimum Factor of Safety on Tensile Overstress 1.0 Minimum Factor of Safety on Geogrid Pullout 1.5 (peak load criterion) Minimum Factor of Safety on Geogrid Pullout 1.0 (serviceability criterion) Minimum Factor of Safety on Facing Shear 1.5 (peak load criterion) Minimum Factor of Safety on Facing Shear 1.0 (serviceability criterion) Minimum Factor of Safety for Connections 1.5 (peak load criterion) Minimum Factor of Safety for Connections 1.0 (serviceability criterion) Minimum Factor of Safety for Uncertainties External Stability of Walls: Minimum Factor of Safety Against Base Sliding 1.5 (static condition) Minimum Factor of Safety Against Overturning 2.0 Minimum Factor of Safety for Global Stability 1.5 Minimum Factor of Safety for Bearing Capacity Design shall address hydrostatic loading, seismic loading, rapid drawdown, surcharge, velocity effects, and back slopes where appropriate SEGMENTAL RETAINING WALL UNITS A. CSRW units shall meet all physical and performance criteria set forth in this specification and the construction shop drawings. CSRW units made by the following manufacturers have been determined to meet the requirements of this specification inch depth Anchor Vertica Pro, as manufactured by Pavestone Anchor Wall Systems. 2. Compact Unit, as manufactured by Keystone Retaining Wall Systems. B. CSRW units shall meet the following structural requirements: 1. Concrete used to form all CSRW units including cap units shall have a minimum net 28- day compressive strength of 3,000 psi. The CSRW units shall have adequate freeze/thaw protection, as indicated by a maximum absorption rate of 8 percent. 2. Cementitious materials used in the manufacture of the units shall be Type I, Type II or Type III Portland cement in accordance with ASTM C Other constituents: Air entraining agents, coloring pigments, integral water repellents, finely ground silica and other constituents previously established as suitable for use in segmental retaining wall units, conforming to applicable ASTM Standards or shown by test or experience to be not detrimental to the durability of the segmental concrete facing units or to any material used in masonry construction. Concrete Segmental Retaining Wall

5 4. Exterior dimensions of units may vary in accordance with ASTM C 90. CSRW concrete facing unit dimensions shall not differ more than " 1/8 inch from the manufacturer s molded dimension, nor more than 1/16 inch in height from front to back of unit. 5. CSRW units shall provide a minimum weight equivalent to 125 pcf. Unit fill placed within the dimensions of the units may be considered as 80 percent of the effective unit weight. 6. Only CSRW Systems with positive interlocking fascia connections such as pins, locators, lips, keyways, or clips are acceptable. 7. If fiberglass connecting pins are required, the pins shall be 2 diameter thermoset isopthalic polyester resin-protruded fiberglass reinforcement rods, with a minimum flexural strength of 128,000 psi and a short beam shear of 6,400 psi. C. FINISH AND APPEARANCE All CSRW 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 construction. D. SAMPLING AND TESTING Compressive strength test specimens shall conform to the saw-cut coupon provisions of Section of ASTM C 140 with the following exception: 1. Coupon shall have a minimum thickness of 1-1/2 inches BASE LEVELING PAD MATERIAL AND UNIT FILL FOR BLOCK A. Base Leveling Pad Material: For channel walls, the base leveling pad material shall be either an extension of the 6 concrete channel lining, or lean, unreinforced Class E concrete 6 thick. For overbank walls, the base leveling pad shall be lean, unreinforced Class E concrete 2 thick or compacted granular fill as specified in Division 31 Section COMPACTED FILL. The base leveling pad shall be constructed to the elevations shown in the approved construction shop drawings. B. Unit Fill: Fill for units shall consist of granular fill as specified in Division 31 Section COMPACTED FILL. C. Drainage Backfill: For all CSRW wall sections, place a minimum of 12 of granular fill behind the CSRW units, as shown in the Contract Drawings and construction shop drawings REINFORCED WALL BACKFILL A. Soils with more than 35% passing the No. 200 sieve, soils with Plastic Index greater than 10, soils with Angle of Internal Friction less than 30 degrees as indicated by Consolidated Drained Triaxial Testing and soils not free of organic material shall not be permitted for use in the reinforced zone. B. Wall backfill material reinforced with geogrid shall have a ph in the range of 3 to 10 as determined in accordance with ASTM G51. C. Do not run mechanical vibrating plate compactors on top of the CSRW units. Compaction of fill between CSRW units and the three foot zone behind the CSRW units shall be accomplished by running hand-operated compaction equipment just behind units. Compact fill to minimum 95% Standard Proctor Density (ASTM D 698). D. The reinforced backfill shall be placed in maximum 8-inch-thick compacted lifts, and shall be compacted to a minimum of 95% Standard Proctor Density (ASTM D 698). Concrete Segmental Retaining Wall

6 E. Furnish to the ENGINEER a Certificate of Compliance certifying that the reinforced backfill materials comply with this section of the specifications RETAINED BACKFILL OR COMMON BACKFILL A. Soil placed behind the reinforced backfill shall be general earth backfill, as described in Division 31 Section COMPACTED FILL. B. Retained backfill shall be compacted as recommended in Division 31 Section COMPACTED FILL EXECUTION 3.01 EXCAVATION A. Excavate to the lines and grades shown on the Drawings. Take precautions to minimize over-excavation. Over-excavation shall be filled with approved compacted material at the CONTRACTOR s expense. Do not to disturb embankment materials beyond the lines shown on the Drawings. B. Excavation of unsuitable soils and replacement with approved compacted material shall be performed in accordance with Section 31, COMPACTED FILL. Contractor s Professional Engineer responsible for design of the CSRW wall shall inspect the excavation and furnish a report approving the subgrade prior to placement of leveling pad material. C. Over-excavated areas in front of wall face shall be filled with approved compacted material at the CONTRACTOR s expense before the wall is built to over four feet in height. D. Verify location of existing structures and utilities prior to excavation. Ensure all surrounding structures are protected from the effects of wall excavation. E. Coordinate installation of new utilities and improvements to existing utilities with wall installation. F. In areas where soft, disturbed or otherwise unsuitable soils are encountered within the zone of influence of the wall loading in the excavations, such unsuitable soils shall be overexcavated to the depths and extent indicated in the contract documents and replaced with suitable material as described in Section 31, COMPACTED FILL LEVELING PAD CONSTRUCTION A. Leveling pad shall be placed as shown on the construction shop drawings. The leveling pad should extend laterally a minimum distance of 6 inches from the toe and heel of the lower most CSRW unit. B. Foundation soil for the leveling pad shall be proof rolled and the top 12 inches compacted to minimum 95% Standard Proctor Density (ASTM D 698) and tested prior to placement of leveling pad materials. C. For overbank walls, compacted granular fill is allowable. The granular leveling pad material shall be compacted to provide a level hard surface on which to place the first course of CSRW units. Well-graded sand can be used to smooth the top 2 to 3 inch of the leveling pad. Alternatively, use a bed of mortar on top of the leveling pad to level the first course of CSRW units. Compaction will be with mechanical plate compactors to minimum 95% of Standard Proctor Density (ASTM D 698). Concrete Segmental Retaining Wall

7 3.03 CSRW UNIT INSTALLATION A. First course of CSRW units shall be placed on the leveling pad. The CSRW units shall be leveled side-to-side, front-to-rear and aligned with adjacent units. The first course is the most important to ensure accurate and acceptable results. Ensure CSRW units are in full contact with the leveling pad. B. Place the front of the CSRW units side-by-side, and shall not leave gaps 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. Layout of curves and corners shall be in accordance with CSRW manufacturer s installation guidelines. C. Install fascia block connections per CSRW manufacturer s recommendations, and place fiberglass connecting pins (if required). Fill all voids of CSRW units with unit fill and tamp fill. D. Place and compact drainage fill between and behind units, and place and compact infill soil behind drainage fill. E. Sweep all excess debris from top of units and install next course. Ensure that each course is completely unit filled, backfilled, and compacted prior to proceeding to the next course. F. Repeat procedure to the extent of wall height, checking alignment every 3 courses to ensure level rows of CSRW units. Stacking of CSRW units without placing core fill in the previous course of units will not be permitted. G. As appropriate where the top of the wall changes elevation, units can be stepped with grade or turned into the embankment with a convex return end. Provide appropriate buried units on compacted leveling pad in the area of the convex return end CAP INSTALLATION A. Place CSRW Cap units per manufacturer s recommendations. Backfill and compact to finished grade. B. Permanent mechanical connection of Cap units to CSRW units shall be provided by construction epoxy. Apply adhesive to bottom surface of Cap unit and install on CSRW units below. Adhesive shall be as recommended by the CSRW manufacturer. END OF SECTION Concrete Segmental Retaining Wall