506Mechanically Stabilized Earth Retaining Structures

506.1 Description

This Work consists of designing, furnishing all Materials, and constructing mechanically stabilized earth (MSE Panel Walls) retaining Structures in acco rdance with these Specifications and in complianc e with the lines and grades, dim ensions and details shown in the Contract.

506.2 Materials

506.2.1 Precast Concrete Elements

The Contractor shall provide precast concrete panel elements co nforming to Section 517, “Precast Concrete Structures.” The Contractor shall provide Cl ass AA concrete. The concrete mix design shall be prepared in accordance with Section 509, “P ortland Cement Concrete Mix Design” and approved by the State Materials Bureau.

506.2.1 1 Casting

For precast concrete face panels, the Contractor shall place th e panel forms on a horizontal surface with the front face of the panel at the bott om of the form. The Contractor shall set connection hardware in the rear face. The Contractor shall place the concrete in each precast concrete panel form without interruption and conso lidate it with an approved vibrator and hand tamping to force the concrete into the corner of the forms and eliminate the formation of stone pockets or cleavage planes. The Contractor shall use clear form oil throughout the casting operation.

506.2.1 2 Finish

506.2.1 2.1 Non-exposed Surfaces

The Contractor shall screed the rear faces of precast concrete panels to create a uniform surface texture that is free of open pockets of aggregates and surface distortions greater than 3/16 inch. The Contractor shall apply a Class I finish, per Se ction 511, “Concrete Structures,” to other non-exposed surfaces.

506.2.1 2.2 Exposed Surfaces

The Contractor shall provide the type of finish on the exposed surface per the Contract. If the Contract requires an exposed aggregate finish, the Contr actor shall produce as follows: 1. Before placing concrete, apply a set retarder to the casting forms in accordance with the manufacturer’s instructions; 2. After removing the forms and after the concrete has set suff iciently to prevent dislodging, expose the aggregate with a combination of brushing and washing (using clean water) to a depth of between 3/8 inch and 1/2 inch ; and 3. Apply an acrylic resin sealer , consisting of 80% thinner and 20% acrylic solids by weight, to the exposed aggregate surface at a rate of one (1) g al per 250 ft 2.

506.2.1 3 Tolerances

The Contractor shall manufacture the precast concrete elements in accordance with the following tolerances: Section 506: Mechanically Stabilized Earth Retaining Structures Page 306 1. Dimensions within precast c oncrete panels, ± 0.2 inch; 2. Surface defects: 2.1. Smooth formed surfaces not greater than ± 3/16 inch within five (5) feet; 2.2. Textured-finish surfaces not greater than ± 5/16 inch with in five (5) feet; and 3. Differences in diagonal lengths not greater than 1/2 inch.

506.2.1 4 Identification and Markings

The Contractor shall inscribe the manufacture date, the product ion lot number, and the piece mark on a non-exposed surface of each element.

506.2.1 5 Handling, Storage, and Shipping

The Contractor shall handle, store, and ship units in a manner that prevents damage and discoloration.

506.2.1 6 Compressive Strength

The Contractor shall not ship or place elements in the wall unt il the design strength is reached. The Contractor shall cast wall panels on a flat area and fully support them until the concrete reaches a minimum compressive strength of 1,500 psi as determined by the Maturity Method detailed in Section 510.3.5.2, “In-Place Concrete Streng th Measurements.” Unless otherwise specified by the wall manufacturer, the Contractor sh all not handle the elements until they reach a compressive strength of 1,500 psi.

506.2.1 7 Rejection

The following defects are suffi cient cause for rejection: 1. Connection defects and out-of- tolerance connection imbeds/in serts; 2. Defects indicating imperfect molding; 3. Defects indicating honeycom bing or open texture concrete; 4. Cracked or severely chipped panels; 5. Color variation on front face of panel due to excess form oi l or other reason; and 6. Presence of oil on panels.

506.2.2 Reinforcing Steel

The Contractor shall provide reinforcing steel in accordance wi th Section 540, “Steel Reinforcement.”

506.2.3 Soil Reinforcement

The Contractor shall provide galvanized steel soil reinforcemen t. Geosynthetic soil reinforcement will not be allowed. The Contractor shall provid e galvanized steel connection hardware in accordance with AASHTO M 111. The Contractor shall support the soil reinforcement while lifting and placing so that the galvanizati on remains intact and does not crack.

506.2.3 1 Steel Reinforcing Strips

The Contractor shall hot roll reinforcing strips from bars to t he required shape and Section 506: Mechanically Stabilized Earth Retaining Structures Page 307 dimensions. The Contractor shall provide reinforcing strips wi th physical and mechanical properties in accordance with AASHTO M 223M, Grade 65, or equiv alent. The Contractor shall provide shop-fabricated tie strips of hot rolled steel in accordance with ASTM A 1011, Grade 50, or equivalent. The mi nimum bending radius of the tie strips is one (1) inch. The Contractor shall apply galvanizati on after strip fabrication.

506.2.3 2 Steel Reinforcing Bar Mats

The Contractor shall provide reinforcing bar mats of cold-drawn steel wire in accordance with AASHTO M 32 and weld the mats into the finished mesh fabri c in accordance with AASHTO M 55. The Contractor shall form mesh button heads so th at variations between the longest and shortest wire in any mesh is less than one (1) inch . The Contractor shall apply galvanization after mesh fabrication. The Contractor shall pro vide a one (1) inch coil embed of cold drawn steel wire in accordance with AISI C 1035.

506.2.4 Connector Pins

The Contractor shall provide c onnector pins and mat bars from A -36 steel and weld to the soil reinforcement mats. The Contractor shall provide connecto r bars of cold drawn steel wire in accordance with AASHTO M 32.

506.2.5 Precast Concrete Panel Fasteners

The Contractor shall provide fa steners in accordance with the C ontract or the approved Working Drawings. The Contractor shall cast fasteners in the p recast concrete panels so that the fasteners are in alignment and will result in fasteners tra nsferring a full and even load to the steel grid or steel strap reinforcement. The tolerance bet ween the fastener and the steel reinforcement grid or steel straps for field installation is 3/ 16 inch. The Contractor shall provide galvanized steel fastener s in accordance with AASHTO M 164.

506.2.6 Precast Concrete Panel Joints

Where walls wrap around a corner, the Contractor shall provide a corner block panel with flange extensions that will allow differential movement without exposing the panel joints. The Contractor shall provide joint filler, bearing pads, and filter fabric in accordance with the wall manufacturer’s recommendations and the approved Working Drawing s. If required, the Contractor shall provide flexible foam strips for filler in vertical joints between panels, and in horizontal joints where pads are used, i n accordance with the Plans. The Contractor shall provide the following for horizontal joint s between panels: 1. Pre-formed Ethylene Propylene Diene Monomer (EPDM) rubber pa ds in accordance with ASTM D 2000 for 4AA, 812 rubbers; 2. Neoprene elastomeric pads having a Durometer Hardness (ASTM D 2240) of 55 ± 5; or 3. High-density polyethylene pads with a minimum density of 60 lb per cubic foot in accordance with ASTM D 1505. The Contractor shall cover the joints between panels on the bac kside of the wall with a geotextile meeting the requirements for filtration applications in accordance with Section

604.2 4, “Separator Geotextile, Class 3.” The Contractor shall provide a minimum lap width of

one (1) ft.

506.2.7 Reinforced Fill Material

Section 506: Mechanically Stabilized Earth Retaining Structures Page 308 The Contractor shall provide backfill Material that is free of shale, organic matter, and other soft particles of poor dura bility. No salvaged Material, such as asphaltic concrete millings, Portland Cement Concrete rubble, etc. will be allowed . The Contractor shall provide backfill with a soundness loss of 30 or less if tested in accordance with AASHTO T 104 using a magnesium sulfate solution with a test duration of four (4) cycles. The Contractor shall determine gradations in accordance with AASHTO T 27 and Table 506.2.7:1, “Backfill Gradation Requirements,” unless otherwise specified. Table 506.2.7:1 Backfill Gradation Requirements Sieve size % passing Four (4) inch 100 No. 40 0 60 No. 200 0 15 The Contractor shall provide backfill with a PI, no greater tha n six (6) in accordance with AASHTO T 90. The Department defines “rock backfill” as the Material that is composed primarily of rock fragments (Material having less than 15% passing a 1/2 inch sie ve and no more than five percent (5%) passing a No. 4 siev e). If using “rock backfill,” the Contractor shall place a separator geotextile over the top of the backfill Material befo re placing the top two (2) ft of backfill. Also, the Contractor shall place a separator geotext ile between the rock backfill and the random fill as the reinforced soil backfill is placed. The Contractor shall provide a separator geotextile in accordance with the minimum requirement s for filtration applications in AASHTO M 288 and Section 604, “Soil and Drainage Geotextiles.” The Contractor shall ensure the upper two (2) ft of backfill does not contain stones larger than three (3) inches at their greatest dimension and is free of rock backfill.

506.2.7 1 Internal Friction Angle Requirement

The Contractor shall provide backfill that e xhibits a minimum a ngle of internal friction of at least 34° in accordance with AASHTO T 236 unless otherwise spec ified in the Contract. The Contractor shall perform the te st on backfill Material passing the No. 10 sieve. The Contractor shall compact the sample in accordance with Section 506.3.5.1, “Compaction,” at optimum moisture content, to 95% of maximum density. The Department wi ll not require direct shear testing for backfills when the gr adation is less than 20% passi ng a 3/4 inch sieve. The Contractor shall submit a M aterials test report to the Proj ect Manager, prepared by an independent Laboratory accredited through the AASHTO Materia ls Reference Laboratory (AMRL), or other Department approved accreditation program, ind icating that the internal friction angle of soil meets or exceeds the requirements specif ied in the Contract. The Contractor shall prepare the test report in accordance with app licable AASHTO Test Standards.

506.2.7 2 Electrochemical Requirements

The Contractor shall provide backfill in accordance with Table 506.2.7.2:1, “Electrochemical Requirements for Steel Reinforcement,” when using steel soil reinforcement. Table 506.2.7.2:1 Electrochemical Requirements for Steel Reinforcement Section 506: Mechanically Stabilized Earth Retaining Structures Page 309 Characteristic Requirement Test method pH 5–10 AASHTO T 289 Resistivity >2,500 ohm/cm AASHTO T 288 Chlorides <100 ppm AASHTO T 291 Sulfates <200 ppm AASHTO T 290 Organic content <one percent (1%) AASHTO T 267 The Department will not require electrochemical testing for bac kfills when the gradation is less than 20% passing a 3/4 inch sieve and less than five perce nt (5%) passing the No. 200 sieve. No salvaged Material, such as asphaltic concrete millin gs, Portland Cement Concrete rubble, etc. will be allowed. The Contractor shall submit a M aterials test report to the Proj ect Manager, prepared by an independent Laboratory accredited through the AASHTO Materia ls Reference Laboratory (AMRL), or other Department approved accreditation program, ind icating that the soil Material meets the requirements specified in the Contract. The Contract or shall prepare the test reports in accordance with the applicable AASHTO Test Standards referenced in the table above.

506.2.8 Cast-in-Place Concrete

The Contractor shall provide cast-in-place concrete in accordan ce with Section 509, “Portland Cement Concrete Mix Des igns,” Section 510, “Portland Cement Concrete,” and Section 511, “Concrete Structures.” Unless otherwise approved, the Contractor shall use Class A concrete for ca st-in-place concrete.

506.2.9 Reserved

506.2.10 Submittals

The Contractor shall ensure a New Mexico registered Engineer si gns and seals Working Drawings and Design Calculations.

506.2.10 1 Working Drawings

The Contractor shall submit Working Drawings to the Project Man ager, for review and approval by the State Bridge Engineer at least 40 Days before b eginning Work on MSE retaining Structures. The Contractor shall submit three (3) co mplete sets of half-size prints for preliminary review. The State Bridge Engineer will return one (1) set of prints to the Contractor with notations. The Contractor shall make necessary corrections and submit eight

506.2.10 2 Design Calculations

Along with the Working Drawing s ubmittals, the Contractor shall submit complete design calculations, including those re quired to establish service lif e, to the Project Manager for approval by the State Geotechnica l Engineer for approval. The Contractor shall ensure the calculations confirm that the proposed design satisfies the des ign parameters in accordance with the Contract and the following: 1. FHWA NHI-10-024 Vol I and NHI-10-025 Vol II, “Design of MSE Wal ls and Reinforced Slopes,” (Berg et al., 2009); and 2. Current "AASHTO LRFD Bridge Design Specifications,” (and interi ms). The Contractor shall provide Structures meeting the requirement s of Table 506.2.10.2:1, “Design Parameters”, unless othe rwise specified in the Contract . Table 506.2.10.2:1 Design Parameters Description Value Resistance Factor Limit State Sliding Strength (all) bBearing Strength (all) bDeep Seated Stability Service I bCompound Stability Service I Pullout resistance Static Strength (all ) Combined static/earthquake Strength (all) Tensile resistance of metallic reinforcements and connectors Static Strip and Grid reinforcement Strength (all) Combined static/earthquake Strip and Grid reinforcement Strength (all) Current AASHTO LRFD Bridge Design Specifications Section 11 Service life 75 years Service life (supporting Structure loads) 100 years Soil unit weight (retained ) 120 lb/ft Soil unit weight (reinforced) 125 lb/ft3 Friction angle (retained soil) 30° Friction angle (reinforced soil) 34° Coefficient of sliding friction a Section 506: Mechanically Stabilized Earth Retaining Structures Page 311 Table 506.2.10.2:1 Design Parameters Description Value Allowable bearing pressure a Minimum soil reinforcement embedment depth a aIn accordance with the Contract. bGlobal Stability is responsibility of NMDOT

506.2.10 3 Certificates of Compliance

The Contractor shall provide the Project Manager with a Certifi cate of Compliance for the Material (excluding concrete) t hat certifies that the Material is in accordance with the Contract and the approved Working Drawings. 506.2.10.4 Reinforced Fill Material Test Reports The Contractor shall submit a complete Materials test report to the Project Manager, prepared by an independent Laboratory accredited through the AA SHTO Materials Reference Laboratory (AMRL), or other Department approved accreditation p rogram, indicating that the soil and/or rock Material meets the requirements specified in t he Contract. The Contractor shall prepare the gradation, fri ction angle (direct shear), and electrochemical test reports in accordance with the applicable AASHTO or ASTM Test Standards.

506.2.10 5 Exposed Surface Finish Panel Sample

If the Contract requires an exposed aggregate or other architec tural finish, the Contractor shall deliver a 36 inch × 36 in ch panel, finished as specified, to the Project Manager for approval by the Landscape Architect.

506.3 Construction Requirements

506.3.1 Excavation

The Contractor shall perform wall construction excavation as un classified excavation in accordance with Section 203, “Excavation, Borrow, and Embankmen t.”

506.3.2 Foundation Preparation

The Contractor shall Grade the foundation for the structural vo lume level for the entire area of the base of the Structure plus 12 inches on all sides, or as shown in the Contract. Before wall construction, the Contractor shall break up the ori ginal ground surface to at least six (6) inches by plowing or sca rifying. The Contractor shall compact this area to 95% of maximum density in accordance with Section 203.3.6, “Moisture a nd Density Control.” The Contractor shall remove uns uitable foundation Material, rep lace with suitable Material meeting the requirements of Section 506.2.7, “Reinforced Fill M aterial,” and compact in accordance with this Specification unless otherwise approved by the State Geotechnical Engineer.

506.3.3 Concrete Leveling Pad

The Contractor shall provide a leveling pad in accordance with the approved Working Drawings. The Contractor shall cure the pads at least 12 hours before placement of wall panels. Section 506: Mechanically Stabilized Earth Retaining Structures Page 312

506.3.4 Wall Erection

The Contractor shall erect walls in accordance with the manufac turer’s written instructions. The Contractor shall ensure that a field represe ntative from the manufacturer is available during the erection of the first ten percent (10%) of the wall (and as directed by the Project Manager) to assist the Fabricator, Contractor, and Proj ect Manager. The Contractor shall place panels so that their final position is vertical or battered in accordance with the Contract. The Contractor shall sequence the placement of panel s in successive horizontal lifts during backfill placement in accordance with the Working Drawin gs.

506.3.4 1 Placement Tolerances for Precast Elements

When placing backfill Material, the Contractor shall maintain p recast elements in the specified vertical alignment with temporary wedges or bracing a s recommended by the manufacturer. The Contractor shall ensure that vertical and ho rizontal alignment tolerances do not exceed 0.75 inch if measured with a ten (10) foot straig htedge. The Contractor shall ensure that the overall horizontal tolerance (plumbness) of the vertical wall does not exceed 0.5 inch per ten (10) feet. The Contractor shall ensure that t he offset at any panel joint does not exceed 0.4 inch.

506.3.4 2 Placement of Reinforcement Elements

The Contractor shall install t he reinforcement elements normal to the face of the wall, unless otherwise shown on the Plans. The Contractor shall ensu re that the reinforcement bears uniformly on the compacted reinforced soil from the conne ction to the wall to the end of the reinforcing elements. The Contractor shall not cut the rei nforcement elements to accommodate obstructions within the reinforced soil zone. The Contractor shall not weld soil reinforcements (shop or field welds) to extend lengths of longi tudinal reinforcements. The Department will allow approved shop welds at the connections an d approved spot-welds at the transverse and longitudinal intersections of bar mats.

506.3.5 Backfill Placement

The Contractor shall perform backfill placement immediately aft er erecting each level of wall panels. The Contractor shall place backfill carefully to avoid damage or disturbance of the wall Materials, misalignment of wall panels, or damage to s oil reinforcement. The Contractor shall replace wall Materials damaged during backfill placement at no additional cost to the Department. If backfill placement causes misalignment o r distortion of wall panels, the Contractor shall correct at no additional cost to the Departmen t.

506.3.5 1 Compaction

The Contractor shall compact ba ckfill in accordance with AASHTO T 180 (Modified Proctor), Method D (TTCP Modified), Note 7, to 95% of the maxim um density, except as modified in accordance with Sec tion 506.3.5.1.2, “Compaction Ag ainst Faces of Walls.”

506.3.5 2 Compaction Against Faces of Walls

The Contractor shall compact the backfill to 90% density as det ermined by AASHTO T 180 (Modified Proctor), Method D (TTCP Modified), within three (3) ft of the wall. The Contractor shall compact with a minimal number of passes using a lightweight mechanical tamper, roller, or vibratory system. The Contractor shall dete rmine the number of passes with a test section before compaction against the wall, as approved by the Project Manager. The Contractor shall use approved com paction Equipment from the tes t section for production Section 506: Mechanically Stabilized Earth Retaining Structures Page 313 Work. If changing Equipment, the Contractor shall create a new test section to determine the number of passes for the Project Manager’s approval.

506.3.5 3 Moisture Control

The Contractor shall uniformly distribute the moisture content of the backfill Material throughout each layer before and during compaction. The Contra ctor shall ensure that backfill Materials have an in-place moisture content of three percent (3 %) less than optimum to optimum. The Contractor shall remove backfill Material with in -place moisture content greater than optimum and rework, or replace with Acceptable backfill Ma terial.

506.3.5 4 Lift Thickness

The Contractor shall ensure that the maximum lift thickness aft er compaction does not exceed eight (8) inches. The Contractor shall decrease the lif t thickness, if necessary, to obtain the specified density.

506.3.5 5 Protection of the Work

At the end of each Day’s operation, the Contractor shall slope the last level of backfill away from the wall to direct runoff away from the Structure. T he Contractor shall not allow surface runoff from adjacent areas to enter the wall constructi on site.

506.4 Method of Measurement

The Department will measure the face of MSE Panel Walls based o n the dimensions shown in the Contract or approved modifications. The Department will measure authorized Excavation of Unsuitable Foundation Material from the foundation surface to the depth of excavation in its o riginal location. The Department will not measure Material excavated outside the area bounded by vertical planes two (2) feet beyond the limits of the Material designated for removal.

506.5 Basis of Payment

Pay Item Pay Unit MSE Panel Wall Square Foot Excavation of Unsuitable Foundation Material Cubic Yard

506.5.1 Work Included In Payment

The Department will consider the following Work as included in the payment for the pay item(s) and will not measure or pay separately for the following: 1. Excavation for MSE retaining Structures including any requir ed temporary shoring; 2. Temporary shoring required for excavation of unsuitable foundation Material; 3. Placement and compaction of backfill Material within the rei nforced soil zone, backfill within the limits of unsuitable foundation Material excavation, and/or other areas identified in the Contract; 4. Dewatering for excavation of MSE Retaining Structures and/or dewatering for authorized excavation of unsui table foundation Materials; 5. Leveling pads, facing elements, reinforcing bars, soil reinf orcements, attachment devices, backfill, coping, drainag e elements, foundation prepar ation, and geotextile Section 506: Mechanically Stabilized Earth Retaining Structures Page 314 fabric; 6. Providing the manufacturer’ s field representative; and 7. Survey, calculations, engineering, and reporting. Section 509: Portland Cement C oncrete Mix Designs Page 315