450 RETAINING WALLS

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450.01 DESCRIPTION
Construct cast-in-place reinforced concrete footings and stems conforming to the AASHTO definitions of rigid retaining walls. When retaining wall mounted noise barriers are specified, the anchorage assemblies are included in the retaining wall. All components shall be as specified unless prior approval for alternatives is obtained from the Administration.
When piles or drilled shafts (caissons) are specified, refer to Sections 410 and 412, respectively.
450.01.01 Preapproved Alternate Retaining Walls. Alternate retaining walls may only be used when specified. Only those retaining walls specified will be permitted. All other retaining walls, even though they are preapproved or have been previously used on Administration projects, are prohibited for use. The Administration will not consider any other alternate retaining walls as a value engineering change proposal.
Enforcement. These requirements will be enforced on all projects.
Preapproved Alternate Retaining Wall List. Alternate retaining walls are selected from the list of Preapproved Alternate Retaining Walls, which is maintained by the Office of Structures. Procedures for adding products to the prequalified list may be obtained from the Office of Structures.
Alternate retaining walls that have been previously used on Administration projects without complying with the preapproval requirements shall be formally submitted through these procedures before they will be added to the Preapproved Lists for consideration to be used on future projects. These and other retaining wall systems may be submitted for addition to the Preapproved Lists, but the Administration will not permit these submittals to be used on an advertised or awarded project.
Deviations. Submit any proposed deviation in materials, post size or shape; panel size or shape; reinforcing type, size, or placement from what is shown in the Contract Documents or from the preapproved alternate retaining wall details on file in the Administration’s Office of Structures. All costs for reviews, whether the details are accepted or rejected, shall be borne by the Contractor. Any fabrication or creation of any retaining wall element that is a deviation and is made prior to written approval of the Administration shall be at the risk of the Contractor.
Contract Documents for Preapproved Alternates. If electing to use preapproved alternate retaining wall systems, only one type retaining wall may be constructed throughout the Contract. Submit substitute plans, design calculations, and specifications. Plans shall be similar in size and detail to advertised documents. Working drawings from the fabricator are not acceptable as substitute plan submissions. Include drainage details and all revisions required to construct the alternate retaining wall system. A professional engineer registered in the State of Maryland, and who has experience in design of the proposed alternate retaining wall system shall prepare, sign, and seal all plans, calculations, and specifications. The substitute plans shall bear the Administration’s title block and be furnished on reproducible paper, linen, or mylar. Contract Documents for construction of alternate retaining walls shall conform to the practices and procedures of the Office of Structures. These plans will be issued as a Contract revision replacing the Administration’s plans and be kept by the Administration as permanent records. All work pertaining to Contract Documents for preapproved alternates shall be at no additional cost to the Administration.
After substitute plans are approved and issued as a redline revision, submit working drawings bearing the fabricator or supplier’s title block for review and approval to the Administration or directly to the consulting engineer as specified in Section 499.
450.02 MATERIALS
Refer to 420.02. When retaining wall mounted noise barriers are specified, refer to 455.02 for the anchorage materials.
Sample Panel. Refer to Section 456 and the Contract Documents for Architectural Treatment specifications.
Some projects may require a specified surface such as an ashlar stone pattern, or matching a similar structure or stonework in the area. The Contractor may request or the Engineer may direct that the sample of the texture be submitted for approval prior to submission of the sample panel containing the specified stain.
450.02.01 Reinforcement. Epoxy coat reinforcing bars and welded wire fabric in retaining walls that are less than 10 ft from the edge of paved surface (includes shoulders). Coat supports for epoxy coated reinforcement the same as the reinforcing steel.
450.02.02 Backfill for Preapproved Alternates. Use size No. 57 stone as backfill for all preapproved alternate retaining walls, regardless of the type backfill recommended or specified by the retaining wall manufacturer. Use geotextile when specified.
450.02.03 Concrete Stain. 902.18. When a color is specified for the exposed surfaces of the retaining wall, select the producer of the stain from the Qualified Products List (QPL) maintained by the Office of Materials Technology. The color number shall meet AMS-STD-595A.
450.02.04 Textures
(a) Unless otherwise specified, the exposed surfaces of the retaining wall shall receive a special surface treatment as specified in 420.03.07(b).
(b) When a special texture is specified, produce it by using an approved form liner.
450.02.05 Preapproved Alternate Retaining Wall. Match the materials and details as approved and on file in the Office of Structures.
450.03 CONSTRUCTION
Construct retaining walls as shown on the Plans, as specified in 420.03, and herein. Construct alternate retaining walls according to the details and specifications that are on file with the Office of Structures. Should any detail or specification change, the retaining wall firm shall submit the revision for review and approval prior to using that revision on Administration projects. Do not submit revisions for projects that are already bid.
Do not apply any loading to retaining wall concrete until the concrete in that portion has attained a compressive strength of at least 3000 psi. In addition, complete the backfilling prior to placing any other loads on the wall.
450.03.01 Concrete Stain. When stain is specified, apply two coats according to the manufacturer’s recommendations or as directed. Before application, ensure that all surfaces are structurally sound, clean, dry, fully cured, and free from dust, curing agents, form release agents, efflorescence, scale, and other foreign materials.
450.03.02 Anchor Bolt Assemblies. When required, install as specified. Refer to Section 455. Complete all holes and welding required in the assemblies before galvanizing. Keep all assemblies free of oil and mill coatings.
450.04 MEASUREMENT AND PAYMENT
Retaining walls will not be measured but will be paid for at the Contract lump sum price for the pertinent Retaining Wall item. The payment will be full compensation for all piles, caissons, footings, forms and form removal, architectural treatment, reinforcement steel, concrete, curing, anchorage assemblies, stains and coatings, excavation, sheeting and shoring, drainage systems, backfill (including size no. 57 stone and geotextiles for alternate retaining walls), and for all material, labor, equipment, tools, and incidentals necessary to complete the work.
When specific items for Piles for Retaining Walls are included in the Contract Documents, they will be measured and paid for as specified in 410.04.
When specific items for Drilled Shafts (Caissons) for Retaining Walls are included in the Contract Documents, they will be measured and paid for as specified in 412.04.