642Mechanically Stabilized Earth Walls

642.01.01 General. This work consists of constructing mechanically stabilized earth (MSE) walls consisting of

precast concrete panel or segmental block s with metallic o r geogrid soil reinforcements.

642.01.02 Design Requirements . Design MSE retaining walls and ancillary elements associated with the

walls in accordance with the plans and as specified herein. Design MSE walls for a minimum service life of 100 years. Maximum reinforcement loads shall be calculated using the “Simplified Method” according to Subsection

11.10.6 2 of the AASHTO LRFD Bridge Design Specifications.

Design and detail base drains and back drains to collect and remove groundwater before it can enter the reinforced backfill of MSE retaining walls. Installation of the drainage system shall occur only during the placement of MSE backfil l. Provide a constant length of all reinforcement layers within a design section to form a uniform reinforced soi l mass, with the exception of the top two layers of reinforcement. Provide the top two layers of reinforcement with a length of reinforcement that is 1.5 m (5 ft) longer than all other layers below. For geogrid reinforcement layers, provide a reinforcement coverage ratio of 1.0 according to S ubsection

11.10.6 4 of the AASHTO LRFD Bridge Design Specifications.

Where concrete panel walls or wall sections intersect with an interior angle of 130 degrees or less, provide a special vertical corner element panel. The corner element panel shall cover the joint of the panels that abut the corner and allow for independent movement of the abutting panels. Geometry of the MSE walls shown on the plans is based on the external st ability of the wall system as determined by the Department. Be responsible for the internal design of the wall based on the design requirements . Design shall include verification of external stability , internal stability , design of concrete wall panel, and corrosion analysis for metallic soil reinforcements . Incorporate proposed highway surface drainage installations and other project specific requirements into the wall design. Top of wall elevation and alignment shall remain as shown on the plans regardles s of the wall system selected. Depth of wall embedment or length of reinforcement may be increased as required by internal design. Fully document all loading conditions and assumptions used for the wall design. Consider all load cases that may be anticipated to exist during construction and during the service life of the wall due to surcharges, hydraulic conditions, live loads, combinations of the preceding, and obstructions within the reinforced backfill. For each wall design section, provide a design summary that includes design section identification, location, wall geometry (height, backslope, etc.), loadings (traffic loading, hydrostatic, seismic, traffic barrier, etc.), governing design resistance fact ors and level where they occur, and other pertinent information.

642.01.03 Installer Qualifications. Provide a n on-site supervisor having experience in the construction of at

least five transportation related MSE walls within the last three years. Transportation related MSE walls are defined as walls that carry or are adjacent to vehicular traffic and are constructed with MSE reinfor cement in the reinforced structure backfill zone . The on-site supervisor shall have prior experience with the type of wall that will be constructed. The on-site supervisor shall be on the job site the entire time the wall is being constructed. Submit verification of the on-site supervisor’s qualifications containing a summary of the individual’s experience and the respective projects at least 30 days prior to beginning wall construction. Do not begin wall construction until the supervisor ’s qualifications have been approved. 642 MECHANICALLY STABILIZED EARTH WALLS

642.01.04 Submittals. Submit working drawings, calculations, and construction manuals according to

Subsection 105.02. Working drawings and calculations shall be prepared and stamped by a registered Civil Engineer licensed in the State of Nevada. Do not begin wall construction until submittals have been approved.

642.01.05 Pre- Activity Meeting. Before commencement of MSE wall construction, the Engineer may

designate a time and place satisfactory to the Contractor for a pre- activi ty meeting . The pre- activity meeting shall be held not more than 2 weeks in advance of the scheduled wall construction . The approved on-site supervisor and the MSE wall manufacturer’s technical representative shall be present at the pre- activity meeting. Do not commence wall construction until all issues raised at the pre- activity meeting have been addressed to the Engineer’s satisfaction. MATERIALS

642.02.01 General. Material shall conform to the following Sections:

Portland Cement Concrete ................................ ...................................................................................................................... Section 501 Reinforcing Steel ................................ ..................................................................................................................................... Section 505 Portland Cement ...................................................................................................................................................................... Section 701 Water ................................ ................................ ....................................................................................................................... Section 722 Wall systems are patented. Provide for such use by suitable legal agreement with the patentee and pay all costs connected therewith. Portland cement concrete for leveling pads and panels for installa tions in Clark County shall be Class A Modified. Concrete shall be Class AA Modified for all other locations. Concrete shall have a minimum 28 day compressive strength of 31 MPa (4,500 psi) or as otherwise shown on the plans. The geotextile shall be a woven, 100% monofilament fabric and conform to the following: PROPERTY TEST METHOD REQUIREMENT Survivability AASHTO M288 CLASS 2 Permittivity ASTM D4491 ≥ 0.5 sec-1 Apparent Opening Size (AOS) ASTM D4751 0.43 mm Maximum Ultraviolet Stability @ 500 hr , Strength Retained ASTM D4355 ≥ 90 %

642.02.02 Concrete Panel Wall. Use concrete panel wall systems listed in the QPL.

Install panel joint bearing pads of the dimensions and thickness shown in the approv ed working drawings . Ensure that bearing pads placed in horizontal joints between panels are preformed Ethylene Propylene Diene Monomer (EPDM) rubber pads. Submit a manufacturer’s certification that the bearing pad material conforms to ASTM D2000 Grade 2, Ty pe A, Class A with a Durometer Hardness of 55 ± 5, or High Density Polyethylene (HDPE) pads with a minimum density of 0.946 g/cm 3 in accordance with ASTM D1505. Determine the stiffness (axial and lateral), size, and number of bearing pads such that the fin al joint opening shall be 19 ± 6 mm (0.75 ± 0.25 in.). As part of the working drawing submittal, provide substantiating calculations verifying the stiffness (axial and lateral), size, and numbering of bearing pads assuming, as a minimum, a vertical loading at a given joint equal to 2 times the weight of facing panels directly above that level. As part of the substantiating calculations, submit results of certified laboratory tests in the form of vertical load- vertical strain and vertical load- lateral strain curves for the specific bearing pads proposed. The vertical load- vertical strain curve sh all extend bey ond the first yield point of the proposed bearing pad. Maximum area of typical individual panels shall be 4.65 m 2 (50 ft2), unless otherwise shown on the plans. Cast the panels on a flat area. Do not contact or attach the coil embedments, tie strip guides, or other galvanized devices to the panel reinforcing steel. Use clear form oil of the same manufacture throughout the casting operation. MECHANICALLY STABILIZED EARTH WALLS 642 Place the concrete in each unit without interruption and consolidate by the use of an approved vibrator, supplemented by such hand- tamping as may be necessary to force the concrete into the corners of the forms and prevent the formation of stone pockets or cleavage planes. Cure the panels according to S ubsection 501.03.08. Panels exhibiting shrinkage cracking due to improper curing will be rejected. The front face surface shall have an approved finish and the rear face an unformed surface finish. Roughly screed the rear face of the panel to eliminate open pockets of aggregate and surface distortions in excess of 6 mm (0.25 in.). When shown on the plans, construct the exposed face of wall panels with an architectural finish. Before casting the panels, fur nish sufficient test panels to assure that the proper architectural finish has been obtained. The size of test panels shall be the same dimensions intended for use in the wall installation. Manufacture panels within 5 mm (0.2 in.) of all dimensions. Angu lar distortion with regard to the height of the panel shall not exceed 5 mm (0.2 in.) in 1.5 m (5 ft). Surface defects on formed surfaces measured on a length of 1.5 m (5 ft) shall not exceed 2.5 mm (0.1 in.). Acceptance of the panels with respect to com pressive strength will be determined on a lot basis. The lot will consist of all production units (batches of concrete or panels) produced within a week’s or 7 day production operation. Production units will be randomly selected according to the production day sample sizes of Table A and tested for compressive strength. Compression tests will be made on standard test specimens prepared according to Test Method No. Nev. T428. Compressive strength testing will be conducted according to ASTM C39. TABLE A Production Day Quantities Sample Size <25 m3 (<35 yd3) (<50 panels) ................................................................................................................................................................. 1 25-50 m3 (35-70 yd3) (50-100 panels) ................................ ...................................................................................................................... 2 51-115 m3 (71-150 yd3) (101-150 panels) ................................ ................................ ................................................................................ 3 >115 m3 (>150 yd3) (>150 panels) ................................ ........................................................................................................................... 5 When standard test specimens are utilized, a minimum of 5 cylinders will be cast for each production unit sampled. Two of these specimens will be cured in the same manner as the panels and tested at 7 days for determining the strength for shipping and placing the panels . The remaining 3 cylinders will be cured ac cording to Test Method No. Nev T428, Section D.1. and tested at 28 days. A test result will be the average compressive strength of 3 cylinders at 28 days. Acceptance of the lot will be made if all acceptance tests in a lot are greater than 31 MPa ( 4,500 psi) or provided no individual 28 day compressive strength test result falls below 28 MPa ( 4,000 psi) and the average 28 day compressive strength of all test results for the lot equals or exceeds the acceptance limits set forth in Table B. The acceptance l imits of Table B shall also apply to core compressive strength tests results. TABLE B Number of Lot Acceptance Tests Lot Acceptance Limits, MPa (psi) 3 – 7 ................................ ........................................................................................................................... 31 + 0.33 R* (4, 500 + 0.33 R*) 8 – 15 .......................................................................................................................................................... 31+ 0.44 R* (4, 500 + 0.44 R*) >15 ............................................................................................................................................................. 31 + 0.46 R* (4, 500 + 0.46 R*) * R is the difference between the largest and smallest acceptance test result. Units will be subject to rejection due to failure to meet any of the requirements specified above. Panels that are cracked, severely chipped, have defects indicating imperfect molding, or have honeycombed or open texture concrete will be subject to rejection. Clearly mark the date of manufacture, production lot number, and piece mark on the rear face of each panel. Handle, store, and ship panels in such a manner as t o prevent chipping, cracks, fractures, and excessive bending stresses. Support panels in storage on firm blocking to protect the panel connection devices and the exposed exterior finish. 642 MECHANICALLY STABILIZED EARTH WALLS

642.02.03 Segmental Block Wall. Use segmental block wall systems listed in the QPL.

Cementitious materials and aggregates for segmental blocks shall conform to the requirements of ASTM C1372 Sections 4.1 and 4.2. The blocks shall be visually efflorescence free. Use an efflorescence control agent in the concrete mix design . Segmental blocks shall comply with the following requirements: TEST TEST METHOD REQUIREMENT Compressive Strength ASTM C140 34.5 MPa ( 5000 psi) Minimum Water Absorption , % ASTM C140 6 Maximum Freeze -Thaw Loss , %: 40 cycles, 5 of 5 samples passing or 50 cycles, 4 of 5 samples passing ASTM C1262 (3% saline solution) 1.5 Maximum or 2.0 Maximum Furnish certified test report s from an independent testing laboratory for each lot of segmental blocks demonstrating conformance to the requirements listed above. A lot shall consist of any number of segmental blocks of any configuration or dimension manufactured by a producer using the same materials, concrete mix design, manufacturing process and cur ing method. Certified test results for representative block lots shall not have been conducted more than 12 months prior to jobsite delivery. The certified test report shall clearly identify the firm conducting the sampling and testing, the type of block, the date sampled, name of the person who conducted the sampling, the represented lot, the number of blocks in the lot, and the specific test results for each of the stated requirements of this specification. Do not use block s without supporting certified test reports. Cast the blocks in steel molds and in a manner that will ensure uniform production. Place the concrete in each block without interruption and consolidate. Do not ship blocks until they obtain a minimum compress ive strength of 28 MPa (4,000 psi). Use a single style block type of approved color and surface texture t hroughout each wall. Provide a top course of facing units composed of solid precast concrete unit s designed to be compatible with the remainder of the wall. Bond t he finishing course to the underlying facing units with a durable, high strength, flexible adhesive compound compatible with the block material. Blocks shall have a minimum depth (front face to back face) of 200 mm ( 8 in.). The minimum front face thickness of blocks shall be 100 mm ( 4 in.) measured perpendicular from the front face to inside voids greater than 25 cm 2 (4 in.2). The minimum thickness of any other portion of the block shall be 50 mm ( 2 in.). Manufacture blocks such that the length and width of each block is within 3 mm (1/8 in.) and the height is within 1.5 mm (1/16 in.) of the standard values published by the manufacturer . When a broken or fractured face is required, the horizontal dimension of the front face shall be within 25 mm (1 in.) of the theoretical dimension of the indiv idual block shown on the plans. Any of the following defects will be sufficient cause for rejection of the blocks:

642.02.04 Mechanically Stabilized Earth Backfill. Backfill shall be free from organic and otherwise

deleterious materials and conform to the following requirements for the type of reinforcement used: Percent Passing by Mass Sieve Size Metallic Reinforcement Geogrid Reinforcement 100 mm (4 in.) ................................ .............. 100 ....................................................... — 19 mm (3/4 in.) ................................ ............... — ....................................................... 100 425 µm (No. 40) ............................................. 0-60 ...................................................... 0-60 75 µm (No. 200) ............................................. 0-15 ...................................................... 0-15 Requirement Project Control and Source Requirement Tests Test Method Metallic Reinforcement Geogrid Reinforcement Sieve Analysis ................................ ................................ .... Nev. T206 ........................ Above ................................ .. Above Sampling Aggregate ................................ ........................... Nev. T200 ........................... — ......................................... — Plasticity Index ................................ ................................ .... Nev. T212 ....................... 6 Max. .................................. 6 Max. Liquid Limit ................................ ......................................... Nev. T210 ....................... 35 Max. ................................ 35 Max. pH ............................................................................... AASHTO T289 ...................... 5.0-10.0 ................................. 4.5-9.0 Resistivity * ................................ .................................. AASHTO T288 .............. 3000 ohm•cm Min. ............................ — Chlorides ..................................................... AASHTO T291 Method A .................. 100 ppm Max. ............................... — Sulfates ................................ ....................... AASHTO T290 Method B .................. 200 ppm Max. ............................... — * When the resistivity exceeds 5000 ohm -cm, the Chloride s and Sulphates requirements are waived. Backfill shall have a coefficient of uniformity, Cu, that is greater than 4 as determined by ASTM D2487. The backfill shall exhibit an angle of internal friction of not less than 34 degrees, as determined by the Standard Direct Shear Test, AASHTO T236, on the portion finer than the 2 mm (No. 10) sieve, utilizing a sample of the m aterial compacted to 95% of AASHTO T99, Method C or D, at the optimum moisture content. No direct shear testing is required for backfills where 80 percent or more of the material is larger than 19 mm (3/4 in.). The materials shall be substantially free of other soft, poor durability particles. The material shall have a magnesium sulfate soundness loss of less than 30% after four cycles or a sodium sulfate soundness loss of less than 15% after five cycles when tested according to AASHTO T104. The portion of the material finer than the 2 mm (No. 10) sieve shall not have an organic content of more than 1% as measured according to AASHTO T267. Furnish a certificate of compliance and test report by an AASHTO accredited laboratory, certifying that the MSE backfill material complies with requirements of the internal friction angle and the magnesium sulfate soundness. A minimum of two samples at two different locations shall have these two tests conducted. If the measured backfill friction angle in laboratory tests is greater than 38 degrees, the friction angle used for design shall be limited to 38 degrees. Acceptance tests for the requirements of the backfill, except internal friction angle and magnesium sulfate soundness, will be performed by the Department. Produce and separate backfill aggregate into individual stockpiles containing no less than 190 m 3 (250 yd3) and no more than 7,650 m3 (10,000 yd3). Each designated stockpile will be sampled a minimum of 10 days prior to placement. Do not use stockpiled mat erial until given approval.

642.02.0 5 Metallic Soil Reinforcement. Fabricate the soil reinforcing system to the dimensions and

tolerances shown on the approved working drawings. Design metallic reinforcements and connection hardware using the t ime dependant corrosion loss rates specified in Subsection 11.10.6.4 of the AASHTO LRFD Bridge Design Specifications. Steel strip-type soil reinforcement and steel connection hardware shall be hot -dip galvanized after fabrication in accordance with AASHTO M111 (ASTM A123). Bar mat or grid- type soil reinforcement shall be galvanized after fabrication in accordance with ASTM A641. Provide a minimum galvanized coating of 605 g/m 2 (2.0 oz/ft2) or 85 µm (3.4 mils) in thickness . Adequately support steel s oil reinforcement while lifting and placing such that the galvanization remains intact. Repair damage to galvaniz ed coatings in accordance with ASTM A780. Steel strip reinforcement shall be hot rolled to the required shape and dimensions. The steel shall conform to ASTM A572, Grade 65. Welded wire reinforcing for bar mat or grid- type reinforcement shall conform to ASTM A1064. Steel t ie strips shall be hot rolled steel conforming to ASTM A1011, Grade 50 minimum. The minimum bending radius of the tie strips shal l be 9.5 mm ( 3/8 in. ). 642 MECHANICALLY STABILIZED EARTH WALLS Connection hardware shall conform to the requirements shown in the approved working drawings. Connection hardware shall be cast in the precast concrete panels such that all connectors are in alignment and able to transfer full and ev en load to the reinforcement. Once the reinforcement is connected to the panel, the amount of slack shall not exceed 3 mm ( 1/8 in.) between the connector and the reinforcement during field installation. Fasteners shall be hot -dipped galvanized and conform to the requirements of AASHTO M164 (ASTM A325) .

642.02.0 6 Geogrid Soil Reinforcement. Geogrid soil reinforcement shall be as previously approved on

the QPL for either concrete panel or segmental block wall systems. Submit a manufacturing quality control certificate and conformance testing results for geogrid soil reinforcement delivered to the site. Perform sampling and conformance testing according to ASTM D4354. Base geogrid product acceptance on ASTM D4759. For geogrid soil reinforcement, provide conformance testing of ultimate tensile strength, T ult. The quality control certificate shall include roll numbers and identification, sampling procedures, and results of the conformance testing with a description of test methods used. Include a signed certific ation that geogrid soil reinforcement is in conformance with these specifications with the submitted quality control certificate. CONSTRUCTION

642.03.01 General. Grade the foundation for the limits of the MSE wall as indicated on the plans and working

drawings . Compact the foundation to not less than 95% of the maximum density as determined by Test Method No. Nev. T108. The in- place density will be determined by Test Method No. Nev.T102 or T103. Remove foundation soils found to be unsuitable or incapable of sustaining the required compaction and replace with mechanically stabilized earth backfill. Construct concrete leveling pads according to Section 502. Construct leveling pads at the foundation level of the facing element s. Cure the pad for a minimum of 12 hours before placement of facing elements. Construct the top surface of the leveling pad so it is level in both directions. The leveling pad shall not deviate from level by more than 3 mm (1/8 in.) in 3 m (10 ft), except at designated steps in the leveling pad shown on the plans or accepted working drawings. Install an internal drainage system behind the wall as indicated on the plans and working drawings. Place outlet pipes at sags in the flow line, at the low end of the collector pipe, and at other locations as shown or specified. Determine the location and elevation of the internal drainage system and include the details in the working drawings. Form openings for weepholes in precast facing panels prior to casting the panels. Have the wall manufacturer’s technical representative present for the pre- activity meeting and during the construction of the first row of facing elements for each wall and as directed. Incorporate changes to the wall installation procedures as recommended by the technical representative. For each day the technical representative is on site, s ubmit an activity report prepared by the technical representative and signed by the contractor documenting that the observed work in progress conforms to the manufacturer’s recommended installation procedures and providing any recommendations for revision s to the installation procedures . Regardless of allowable wall tolerances, do not construct walls with a negative slope or batter (sloping away from the retained soil ). Do not drill or drive posts (sign, guardrail, etc.) or other roadside hardware through the reinforced backfill after placement of backfill. Install the soil reinforcement in accordance with the wall manufacturer's recommendations, the plans, approved working drawings, and as specified herein. Place the reinforcement within the layers of the compacted backfill material at the locations shown in the working drawings. Only place that amount of reinforcement required for immediately pending wo rk to prevent undue damage. Place reinforcement with the strongest direction oriented perpendicular to th e wall face, unless otherwise shown in the working drawings. Connect the reinforcement to the wall facing as indicated in the details included in the a pproved working drawings. Lay the reinforcement flat and uniformly tension to remove slack in the connection or reinforcement material. After the reinforcement is connected to the panel, the amount of slack shall not exceed 3 mm (1/8 in.) between the connector and the reinforcement during installation. Where wall geometry causes soil reinforcement to overlap, provide a minimum vertical separation of 75 mm (3 in.) between overlapping reinforcements . MECHANICALLY STABILIZED EARTH WALLS 642 Backfill placement shall closely follow the erection of eac h course of panels. Cover reinforcement with backfill during the same work shift that it is placed. At each reinforcement level, roughly level backfill before placing and fastening the soil reinforcement. Place the backfill in uniform horizontal layers not exceeding 200 mm (8 in.) in loose thickness before compaction. Place backfill in horizontal layers not exceeding 150 mm (6 in.) i f using hand- operated compaction equipment . Moisten each layer of backfill as necessary and thoroughly compact to achieve the patentee’s required percentage of maximum density or 95% of maximum density, whichever is greater, as determined by Test Method No. Nev. T108. The in place density will be determined by Test Method No. Nev. T102 or T103. Place backfill in such a manner to avoid damage or disturbance to the wall materials or misalignment of the facing elements. Do not operate construction equipment directly on reinforcement. Maintain a layer of backfill at least 150 mm ( 6 in.) thick between reinforcement and any construction equipment. Backfill shall extend to at least 300 mm (12 in.) beyond the free end of the reinforcement. Do not use sheepsfoot or grid- type rollers for compacting MSE backfill. Compact backfill material located within 1 m (3 ft) of the back face of the wall or a backfill penetration (pile, drainage structure, etc.) using a minimum of three passes of a lightweight walk behind vibratory plate or roller. Ensure that voids do not exist beneath reinforcing elements at the back face of the wall. The moisture c ontent of the backfill material prior to and during compaction shall be uniform. At the end of each day's operations, shape the last level of backfill to direct surface runoff away from the wall face. In addition, do not allow surface runoff from adjacent areas to enter the wall reinforcement zone until this zone is protected from infiltration. Repair damage or movement caused by erosion, sloughing, or saturation of the reinforced backfill.

642.03.02 Concrete Panel Wall . Construct concrete panel walls as described in the wall manufacturer’s

approved construction manual and as described herein. Construct copings according to Section 502. Do not place p anels prior to the panels reaching an age of 7 day s and a compressive strength of at least 85% of the specified 28 day strength requirement . Handle panels by a lifting device set into the upper edge of the panels or as indicated in the working drawings. Place the first course of panels directly on the leveling pad. Provide external bracing for the first lift of panels. As backfill material is placed, maintain the panel in position by means of temporary wooden wedges and clamps or bracing in accordance with the wall m anufacturer’s recommendations. Remove the wedges as soon as the panel above the wedged panel is completely installed and backfilled. Place panels in successive horizontal lifts in the sequence shown on the working drawings as backfill placement proceeds. Adjust panel bracing procedures as necessary to provide the vertical and horizontal alignment shown on the plans and working drawings and conforming to the specified tolerances. Repair damage to installed panels as directed. Final panel joint openings shall be 19 mm ± 6 mm (3/4 ± 1/4 in.). Place geotextile over all panel joints on the back face of the wall including the joint along the leveling pad. The geotextile shall have a minimum width of 300 mm (12 in.) and shall be centered over the joint . Overlap intersecting geotextile layers a minimum of 100 mm (4 in.). Install the geotextile fabr ic by applying adhesive to the back of the panel on each side of the joint. Do not apply adhesive directly on the geotextile fabric or within 50 mm (2 in.) of the panel joint edge. Vertical tolerances and horizontal alignment tolerances shall not exceed 1 9 mm ( 3/4 in. ) when measured along a 3 m ( 10 ft. ) straight edge at any location along the wall . The overall vertical tolerance of the wall (plumbness from top to bottom) shall not exceed 12.5 mm (1/2 in. ) per 3 m (10 ft) of wall height. The allowable out of plane offset between panels at the joint shall not exceed 9.5 mm ( 3/8 in.). 642 MECHANICALLY STABILIZED EARTH WALLS

642.03.03 Segmental Block Wall. Construct segmental block walls according to the approved working

drawings and the manufacturer’s construction manual. Do not stockpile or store materials or large equipment within 3 m (10 ft) of the front face of the wall. Construct the leveling pad as wide as the proposed blocks or a minimum of 300 mm (12 in.). The bottom row of blocks shall be l evel and in full bearing with the leveling pad. For walls that are less than or equal to 1.5 m ( 5 ft) in height, a 300 mm (12 in.) deep by 600 mm (24 in.) wide leveling pad constructed from Type 1 Class B Aggregate Base compacted to 95% according to Section 302 may be used. If any portion of the wall is over 1. 5 m (5 ft) in height , use a concrete leveling pad for the entire length of the wall. Place segmental blocks in successive horizontal lifts in the sequence shown on the approved working drawings. Level the first row of blocks from block -to-block and from front -to-back. Place blocks such that they are snug or to within 1.5 mm (1/16 in.) together and parallel to the straight or curved line of the wall face. Dry-stack all blocks and place each block evenly spanning the joint in the row below (running bond). Shim or grind to control the elevations of any two adjacent blocks to within 1.5 mm (1/16 in.) . Check the top of blocks with a minimum length of 1 m ( 3 ft) long straight edge bubble level. Grind high points identified by the straight edge. Check block front to back tilting frequently, and correct by shimming no later than after 3 completed courses. Install all pins, rods, clips, or other devices used to de velop mechanical interlock between block layers according to the approved working drawings and manufacturer’s construction manual. Fill formed voids or openings in the facing units with core fill consisting of a free- draining, coarse grained crushed stone or granular fill conformi ng to the following gradation: Sieve Size Percent Passing by Mass 38 mm (1.5 in .) ................................ .............................................. 100 25 mm (1 in.) ............................................................................ 75-100 19 mm (3/4 in.) ................................ ............................................ 50-75 4.75 mm ( No. 4 ) ................................ ............................................ 0-60 425 µm ( No. 40) ................................ ............................................ 0-50 75 µm ( No. 200) ................................ ............................................. 0-5 Evaluate the core fill gradation at a frequency of 1 test per 38 m3 (50 yd3) and for every change in material source. The minimum length of soil reinforcement measured from the back face of the wall shall be 70% of the wall height or as shown on the plans or approved working drawings . In no case shall this length be less than 2 m (6 f t). The soil reinforcement shall extend 1 m ( 3 ft) beyond the theoretical failure plane in all cases. The maximum vertical spacing of soil reinforcement layers shall be two t imes the block depth (front face to back face) or 800 mm ( 32 in .), whichever is less. The first (bottom) layer of reinforcement shall be placed no further than 300 mm ( 12 in.) above the top of the leveling pad, but at least one block height above the level ing pad. The last (top) layer of soil reinforcement shall be no further than 600 mm ( 24 in.) below the top of the uppermost block. Each geogrid layer shall be continuous throughout the lengths indicated on the plans. Join geogrid strips with straps, rings, hooks , or other mechanical devices to prevent movement during backfilling operations. Provide a minimum width of 300 mm (12 in.) of core fill behind solid (non- hollow) block units. Place geotextile fabric between the unit (core) fill and the reinfo rced backfill. Do not advance placement of backfill more than the height of the installed block layer until the drainage fill, unit (core) fill, and all fill in all openings within the blocks at that level have been placed. Sweep each layer of facing units clean of all debris before placing the next layer of facing units. Vertical tolerances and horizontal alignment tolerances shall not exceed 19 mm (3/4 in.) when measured along a 3 m (10 ft) straight edge at any location along the wall. The overall vertical tolerance of the wall (plumbness from top to bottom) shall not exceed 32 mm (1 1/4 in.) per 3 m (10 ft) of wall height. MECHANICALLY STABILIZED EARTH WALLS 642 METHOD OF MEASUREMENT

642.04.01 Measurement. Concrete leveling pads will be measured and paid for according to Section 502.

Structure excavation and granular backfill will be measured and paid for according to Sections 206 and 207. Concrete panel walls will be measured by the square meter (square foot), measured on the exterior face of the wall from the top of footing to the top of the coping. Copings for concrete panel walls will be measured by the linear meter (linear foot) along the top of the coping. Concrete panel wall copings integrated with barrier rails or reinforced concrete slabs will be m easured and paid for according to Sections 502 and 505. Mechanically stabilized earth backfill will be measured by the cubic meter (cubic yard). Limits of mechanically stabilized earth wall, mechanically stabilized earth backfill, coping, structure excav ation, and granular backfill shown on the plans are based on external design requirements. Actual limits will be as shown on the approved submittals and no additional compensation will be allowed for quantity increases due to patentees’ internal requirements. Segmental block walls will be measured by the square meter (square foot), measured on the exterior face of the wall from the bottom of the wall to the top of the wall. BASIS OF PAYMENT

642.05.01 Payment. The accepted quantities, measured as provided above, will be paid for at the contract

price per unit of measurement for the pay items listed below that are shown in the proposal. Payment will be full compensation for the work prescribed in this Section. Payment will be made under: Pay Item Pay Unit Concrete Panel Wall ................................ ...................................................................................................... Square Meter (Square Foot) Mechanically Stabilized Earth Backfill ................................................................................................................. Cubic Meter (Cubic Yard) Coping ............................................................................................................................................................... Linear Meter (Linear Foot) Segmental Block Wall .................................................................................................................................... Square Meter (Square Foot) SECTION 643 GROUND ANCHORS DESCRIPTION

643.01.01 General. This work consists of constructing ground anchors for retaining walls.

643.01.02 Qualifications. Prepare a project reference list verifying the successful construction completion of

at least 6 permanent ground anchor retaining wall projects during the past 3 years totaling at least 250 ground anchors. Include a brief description of each project including the location, number of anchors, and the Owner’s name, address, and current phone number. Provide a Nevada Registered Professional Engineer, employed by the ground anchoring Contractor and having experience in the construction of ground anchor retaining walls on at least 6 completed projects during the past 3 years, to supervise the work and pr epare submittals. Consultants or manufacturer’s representatives will not be allowed to satisfy the aforementioned requirement. Use an on- site supervisor and drill rig operators having experience installing ground anchors on at least 4 projects over the pas t 2 years. Prepare a personnel qualifications list containing a summary of each individual’s experience and the respective projects.

643.01.03 Submittals. Submit 5 copies of the following information for review and approval at least 30 days

prior to begin ning wall construction: