423Retaining Walls

2.1 General . Furnish materials in accordance with the following.

 Item 420, “Concrete Substructures”  Item 421, “Hydraulic Cement Concrete”  Item 440, “Reinforcement for Concrete”  Item 445, “Galvanizing”  Item 458, “Waterproofing Membranes for Structures”  Item 556, “Pipe Underdrains” Use concrete for retaining walls that conforms to the requirements of Table 1 unless otherwise shown on the plans . Table 1 Concrete for Retaining Walls Application Concrete Cast-in-place, non -reinforced Class A Cast-in-place, reinforced Class C Precast Class H, f′ c = 4,000 psi Furnish concrete for machine- made concrete block units in accordance with ASTM C90, Class 1, Type II, except the minimum 28- day compressive strength must be 4,000 psi with maximum moisture absorption of 7%. Provide Type 1 filter fabric in accordance with DMS -6200 , “Filter Fabric.” Provide filter fabric rated as UV - resistant when used as part of the exposed facing for a temporary wall . Joint fillers, pads, waterstops, and other incidental materials must be as shown on the plans or approved by the Engineer. Epoxy coat all steel used in concrete panels and coping including connectors, dowels, stirrups, and reinforcing steel when the plans call for epoxy coating of steel earth reinforcements. Construct p ermanent r etaining walls approved for use in accordance with DMS -4800 , “Proprietary Earth Retaining Wall System,” and on the A pproved System L ist for Concrete Block Retaining Walls Systems and Mechanically Stabilized Earth Panel Type Systems.

2.2 Definitions. This Item uses the following terms .

 Permanent Wall . A retaining wall with a design service life of 75 yr. All walls are presumed to be permanent walls unless otherwise shown on the plans.  Temp orary Wall . A retaining wall so designated by description, with a design service life of 3 yr.  Mechanically Stabilized Earth (MSE) Wall . A wall consisting of a volume of select backfill with tensile earth reinforcement elements distributed throughout. Permanent MSE walls use a precast concrete 559 panel as a facing element. Provide the approved MSE panel type systems in accordance with DMS -4800 . Temporary MSE walls use welded wire fabric with filter fabric backing as a facing element.  Concrete Block Wall . A retaining wall that uses machine- made, precast concrete block units as facing elements. The walls may use a volume of select fill with tensile earth reinforcements distributed throughout, or may use only the facing unit and unit fill weight for support. Provide the approved concrete block retaining wall systems in accordance with DMS -4800 .

2.3 Fabrication .

2.3.1 Cast -in-Place. Execute work in accordance with Item 420.

2.3.2 Formed Precast . Execute work in accordance with Item 424, “Precast Concrete Structural Members

(Fabrication).”

2.3.3 Machine- Made Precast . Furnish machine- made concrete block units in accordance with ASTM C90,

sampled and tested in accordance with ASTM C140. Furnish units with molded dimensions within 1/8 in. of specified dimensions, except height must be within 1/16 in.

2.4 Backfill .

2.4.1 Non-Select . Furnish non- select backfill for walls other than temporary and permanent MSE and concrete

block walls as shown on the plans. Non- select fill will be in accordance with Item 132, “Embankment,” of the type shown on the plans. Provide material with a maximum plasticity index of 30 if no type is specified, as determined in accordance with Tex-106-E .

2.4.2 Select . Select backfill is required in specific areas of permanent and temporary MSE and concrete block -type

retaining walls. Provide select backfill that is free of organic or otherwise deleterious materials and that conforms to the gradation limits shown in Table 2, as determined in accordance with Tex-401-A . Provide backfill that does not contain shale, caliche, or other soft, poor -durability coarse aggregate particles. Reclaimed a sphalt pavement is not allowed. Manufactured sand is allowed for temporary walls with a service life of 3 yr. or less. Test each source of backfill for durability and soundness in accordance with Tex-411-A , five-cycle magnesium sulfate soundness. Backfill material with a maxi mum five -cycle soundness loss exceeding 25% will be rejected. Alternately, Tex-461-A Micro -Deval abrasion may be used if the corresponding results show loss is not greater than 20% ; otherwise Tex-411-A governs aggregate verification. Type AS, BS, and DS particles larger than 1/4 in. must be angular or completely crushed. Provide mechanically crushed gravel or stone backfill. Gravel from each aggregate source will have at least 95% two or more mechanically induced crushed faces, as determined in accordance with Tex -460-A , Part I. Rounded rock or rounded gravel is not allowed. Natural sand meeting the requirements of this Section is permitted for use. 560 Table 2 Select Backfill Gradation Limits Type Sieve Size Percent Retained AS 3” 0 1/2” 50–100 #4 See Note #40 85–100 #200 95–100 BS 3” 0 #4 See Note #40 40–100 #200 85–100 CS 3” 0 #4 See Note #200 75–100 DS 3” 0 3/8” 85–100 #200 95–100 Note —Use No. 4 sieve for determination of rock backfill in accordance with Section 2.4. , “Backfill.” When the backfill gradation results in 85% or more material retained on the No. 4 sieve, the backfill will be considered rock backfill. All Type DS backfill is considered rock backfill. In addition to the requirements for Type CS select fill, the plasticity i ndex in accordance with Tex -106-E may not exceed six. Furnish Type BS backfill for permanent walls; Type CS backfill for temporary walls; and Type DS backfill for areas of walls subject to inundation unless otherwise shown on the plans, or below the 100- year flood elevation as shown on the plans. Furnish backfill meeting the requirements of this Section but with a maximum particle size of 3/4 in. when nonmetallic or epoxy coated earth reinforcements are used.

2.4.3 Drainage Aggregate for Concrete Block Wall . Use drainage aggregate to fill the void within concrete block

units and in the zone 1 ft. behind the units. Provide drainage aggregate that is free of organic or otherwise deleterious materials and that conforms to the gradation limits shown in Table 3 as determined in accordance with Tex-110-E . Table 3 Drainage Aggregate Gradati on Limits Sieve Size Percent Retained 1” 0 3/4” 25–50 1/2” 50–100 #4 75–100

2.4.4 Cement -Stabilized Backfill. Use cement -stabilized backfill when required or as approved. Stabilize

Type CS backfill with 5% hydraulic cement by dry weight of the backfill material. Use a stationary plant to thoroughly mix the backfill material, cement, and water. Place and compact the backfill within 2 h r. of mixing. Provide special drainage provisions when cement -stabilized backfill is used, as shown on the plans.

2.4.5 Electrochemical . Provide backfill meeting the following additional requirements for permanent retaining wall

systems using galvanized metallic earth reinforcements .  The pH is between 5.5 and 10.0 as determined in accordance with Tex-128-E .  Resistivity is more than 3,000 ohms centimeter ( ohm-cm) as determined in accordance with Tex-129-E . 561  Material with resistivity between 1,500 and 3,000 ohm-cm may be used if the chloride content is less than 100 parts per million ( ppm) and the sulfate content is less than 200 ppm as determined in accordance with Tex -620-J . Perform electrochemical testing on the raw, unstabilized backfill material when cement -stabilized backfill is used.

2.5 Earth Reinforcements. Furnish earth reinforcements that meet the design requirements. Galvanize or

epoxy coat all steel elements for permanent walls in contact with soil. Epoxy coat in accordance with Item 440, except provide a minimum 18- mil coating thickness. Epoxy coat the reinforcing only when shown on the plans or as approved. Use connection hardware that is likewise nonmetallic or epoxy coated when using nonmetallic or epoxy coated earth reinforcements.

3.1 General . Construct retaining walls as shown on the plans and the approved working drawings, and in

accordance with the following Items .  Item 110, “Excavation”  Item 132, “Embankment”  Item 400, “Excavation and Backfill for Structures”  Item 420, “Concrete Substructures”  Item 458, “Waterproofing Membranes for Structures”  Item 556, “Pipe Underdrains” Construct required piling or drilled shafts in conformance with the pertinent specification.

3.2 Options . When optional design details are shown on the plans, the Contractor is required to use the same

facing design within an area of continuous retaining walls. Provide drawings for review indicating the proposed design arrangement when proposing the use of two or more systems.

3.3 Submittals . When proprietary wall systems are used for permanent or temporary walls, submit working

drawings including casting drawings, construction drawings, and design calculations bearing the seal of a licensed professional engineer for review and approval in accordance with the Department’s Guide to Shop Drawing Submittal s process. Upon completion of construction, submit a set of reproducible as -built drawings.

3.3.1 Casting Drawings . Include all information necessary for casting wall elements, including railing and coping

when prefabricated. Show shape and dimensions of panels; size, quantity, and details of the reinforcing steel; quantity, type, size, and details of connection and lifting hardware; and additional necessary details.

3.3.2 Construction Drawings . Include a numbered panel layout showing horizontal and vertical alignment of the

walls as well as the existing and proposed ground lines. Include all information needed to erect the walls, includi ng the proposed leveling pad elevations; the type and details of the soil reinforcing system (if applicable); the details and manufacturer of all pads, fillers, and filter fabric; the limits and dimensions of structural backfill; details necessary to incorporate coping, railing, inlets, drainage, and electrical conduit; and additional necessary details. Leveling pad elevations may vary from the elevations shown on the plans. Provide at least 1 ft. of cover from the top of the leveling pad to finished grade unless a different minimum cover or a specified minimum leveling pad elevation is shown.

3.3.3 Design Calculations. Include calculations covering the range of heights and loading conditions on the

project. Calculations for both internal and external stability as shown on the plans will be required. Include a 562 summary of all design parameters used; material types, strength values, and assumed allowables; loads and loading combinations; and factor -of-safety parameters.

3.4 Permanent MSE Walls. Grade the foundation for t he structure level to a width equal to or exceeding the

length of the reinforcing system. Perform proof rolling on retaining wall foundation area to identify any loose, soft, or unsuitable materials in accordance with Item 216, “Proof Rolling.” Material not meeting a maximum rut depth of 1 in. per pass of pneumatic tire roller should continue to be rolled or removed and replaced with suitable material. Pneumatic tire rolling will be waived for portions of wall with a reinforcement length of 8 ft.; for these conditions , proof rolling will be required using a smooth- wheeled vibratory roller or other approved roller. Place drilled shafts and piling located within the MSE volume before construction of the wall. Place any required pipe underdrain before construct ion of the wall. Complete MSE wall construction before construction of abutment caps and abutment wing walls. Completion of walls and abutment should be in conjunction with project phasing or allow for completion of walls that meets the proper placement and compaction at abutments. Place the concrete leveling pad as shown on the construction drawings. Provide a wood float finish and wait at least 24 hr. before beginning panel erection. No curing or strength testing of the leveling pad concrete is required. Shim the first row of panels as necessary to achieve correct alignment. Use plastic shims or other material that will not deteriorate. Remove and replace the leveling pad or provide a grout level -up as directed if the required shim height exceeds 1 in. Place filter fabric behind the wall along the joint between the leveling pad and the panels. Grout areas where filter fabric spans more than 6 in. at leveling pad steps. Place and compact fill material over the leveling pad to an elevation even with or above the surrounding ground after backfilling the first row of panels. Do not allow water to accumulate and stand at the base of the wall. Place filter fabric behind all wall joints and at the intersection of retaining walls with other structures, including riprap. Cover joints at least 6 in. on each side and use adhesive to hold the filter fabric in place. Exercise care while lifting, setting, and aligning panels to prevent damage to the panels. Discontinue any operation that results in chipping, spalling, or c racking of panels. Remove and replace damaged panels, or repair as approved. Provide external bracing for the initial row of panels. Use wooden wedges, clamps, or other means necessary to maintain position and stability of panels during placement and compaction of backfill. Remove wooden wedges as soon as the panel or coping above the wedged element is erected and backfilled. Remove all wedges after completing the wall. Review plumbness and position of each row of panels before placing the subsequent r ow. Remove and rebuild any portion of the wall that is out of tolerance. Modify panel batter and bracing, and backfill material, placement, and compaction methods as required to maintain wall tolerances. Construct walls to a local vertical and horizontal alignment tolerance of 3/4 in. when measured along a 10- ft. straightedge relative to vertical and horizontal wall control line. Construct walls to an overall vertical tolerance (plumbness from top to bottom) of 1/2 in. per 10 ft. of wall height. Construct w alls so the maximum offset at any panel joint is between 3/8 in. and 3/4 in. and no joint is open to the extent the filter fabric is visible from the front of the wall. Place backfill to closely follow the erection of each row of panels. Place the select and embankment backfill to the same elevation where possible, and operate the compaction equipment over the interface. Do not 563 create a continuous, distinct, vertical joint between the select and embankment backfill. Complete the embankment after construction of the retaining wall. Maintain the stability of the interface area between the existing ground and the select fill when building a wall against existing ground. Remove and recompact any material that loosens, caves, or fails. Compact backfill to provide at least 95% of density determined in accordance with Tex -114-E . Field density determination will be made in accordance with Tex-115-E . Sprinkle backfill as required to ensure adequate uniformly distributed moisture in each lift before and during compaction. Place fill in lifts of 8 in. or less (loose measurement). Place fill in a manner that avoids segregation of the fill. Decrease the lift thickness if necessary to obtain the required compaction. Use hand- operated or walk -behind compaction equipment in the 3- ft. wide strip adjacent to the wall panels. Do not displace panels or distort or damage the reinforcement system during compaction. Modify backfill material, placement, and compaction methods as necessary to meet density requirements while maintaining wall tolerances. Place rock backfill or material the Engineer determines too coarse for density testing in accordance with Section 132.3.4.1., “Ordinary Compaction.” Place and compact the backfill to the reinforcement level, at each earth reinforcement level, before placing the reinforcement. Place earth reinforcements perpendicular to the face of the wall. Remove slack in connections before placing backfill. Pre- tension each layer of reinforcement to remove slack before placing backfill for systems using nonmetallic earth reinforcements. Use devices capable of mechanically applying and holding the required force. Do not operate tracked equipment directly on any reinforcement. Cover the rock backfill with filter fabric before placing the 2 ft. of backfill immediately below the pavement structure or top of wall when rock backfill is used. Overlap the fabric at least 18 in. at splices, and extend it past the edge of the rock backfill at least 18 in. Use backfill that contains sufficient fines to fill the voids in a compacted state above the filter fabric. Place a horizontal layer of filter fabric as specified above when transitioning from rock backfill to finer grained backfill anywhere within the wall volume. Prevent surface water or rainwater from damaging the retaining walls during construction. Shape the backfill to prevent water from ponding or flowing on the backfill or against the wall face. Remove and replace any portion of the retaining wall damaged or moved out of tolerance by erosion, sloughing, or saturation of the retaining wall or embankment backfill.

3.5 Temporary MSE Walls. Provide a facing system rigid enough to maintain a smooth and straight wall face both during and after construction.

Grade and compact the foundation for the structure in accordance with Section 423.3.4., “Permanent MSE Walls.” Place earth reinforcement and facing system as shown on the approved working drawings. Backfill the 2- ft. zone immediately behind the facing with clean, coarse rock meeting the requirements of Coarse Aggregate Grade 1, 2, or 3 of Item 421, or with Type DS backfill as described in Section 423.2.4.2., “Select.” Cement -stabilized backfill as described in Section 423.2.4.4., “Cement -Stabilized Backfill ,” or crushed concrete may be used in place of the coarse rock. Place and compact backfill in accordance with Section 423.3.4., “Permanent MSE Walls.” Construct walls to a vertical and horizontal alignment tolerance of 3 in. when measured along a 10- ft. straightedge. Construct walls to an overall vertical tolerance (plumbness from top to bottom) of 2 in. per 10 ft. of wall height. Place adjacent facing elements so the maximum out -of-plane offset at any facing element joint is less than 1 in. Place facing elements and filter fabric with no gaps in the facing or fabric. 564 Prevent surface water or rainwater from damaging the retaining walls during and after construction. Place temporary berms or curbs, shape the backfill, or use other approved methods to prevent water from flowing against or over the wall face. Remove and replace any portion of the wall damaged or moved out of tolerance by erosion, sloughing, or saturation of the retaining wall or embankment backfill .

3.6 Concrete Block Retaining Walls. The concrete block units may be sampled and tested by the Engineer before shipment or upon delivery to the construction site. Display samples of block units indicating the color, texture, and finish for approval . Store, tr ansport, and handle all block units carefully to prevent cracking or

damage. Grade and compact the foundation for the structure, and place the leveling pad in Section 423.3.4., “Permanent MSE Walls.” Place the concrete block facing units as shown on the approved working drawings. Fill the voids within the units and fill the 1- ft. zone immediately behind the facing with drainage aggregate as described in Section 423.2.4.3., “Drainage Aggregate for Concrete Block Wall.” Systems tested without unit fill may omit the fill as shown on the approved drawings. Systems with approved filter fabric details may omit the drainage aggregate in the 1- ft. zone immediately behind the facing. Place reinforcements and backfill for walls using earth reinforcements in accordance with the requirements of Section 423.3.4., “Permanent MSE Walls.” Pay particular attention to the connection details of the earth reinforcements to the concrete block units. Construct walls to a vertical and horizontal alignment tolerance of 1 -1/2 in. whe n measured along a 10- ft. straightedge. Construct walls to an overall vertical tolerance (deviation from the vertical or battered control line, top to bottom) of 1 in. per 10 f t. of wall height. Place adjacent facing elements so the maximum out -of- plane offset at any facing element joint is less than 1 in. Place facing elements with maximum 1/4- in. gaps between block units. Prevent surface water or rainwater from damaging the retaining walls during construction. Shape the backfill to prevent water from ponding or flowing on the backfill or against the wall face. Remove and replace all portions of the retaining wall damaged or moved out of tolerance by erosion, sloughing, or saturation of the retaining wall or embankment backfill.