476 — PROTECTION FOR SCOUR AND UNDERMINED AREAS 2026 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS CATEGORY 400 STRUCTURES SECTION 476 — PROTECTION FOR SCOUR AND UNDERMINED AREAS
476.01 Description
Furnish and install grout-filled bags or mats for scour protection and fill undermined areas of structures with grout as specified in the Contract Documents.
476.02 Materials
Geotextile 919, Class SE
476.02.01 Grout shall consist of 846 lb/yd3 of Type II portland cement, mortar, sand aggregate, 6 + 1
percent air entrainment by volume, and water proportioned to provide a pumpable mixture. The 28 day compressive strength shall be a minimum of 3500 psi.
476.02.02 Grout bags/mats shall be made of a high strength water permeable fabric of nylon 6.6
filament fiber. Each bag/mat shall be provided with a self-closing inlet valve to accommodate the insertion of the grout pumping hose. Grout bags shall have a maximum length of 4 ft, a maximum width of 3 ft, and a thickness of 1 ft. Seams shall be folded and double stitched. Ready mixed high strength grout may be permitted with permission of the Engineer. Ensure that the ready mixed high strength grout is furnished by a manufacturer approved by the Administration and as specified in Section 915. Fabric shall exhibit the following properties in both warp and fill directions: TEST PROPERTY TEST METHOD SPECIFICATION LIMITS Tensile Strength, min D 4632, Grab Method 400 lb/in. Tear Strength, min D 4533, Trapezoidal Method 90 lb Permittivity, min D 4491 0.4 sec-1 Apparent Opening Size, min D 4751 0.4 mm 476 — PROTECTION FOR SCOUR AND UNDERMINED AREAS 2026 STANDARD SPECIFICATIONS FOR CONSTRUCTION AND MATERIALS
476.03 Construction
When specified, perform excavation with air lift dredging equipment prior to placement of the grout bags/mats. Place dredged material in dewatering devices specified in the plans or permits. When specified, reuse the dewatered suitable material to fill low points in the same body of water as directed by the Engineer. Otherwise, remove and dispose of dredge material. Use mixers and agitators as specified in 915.03.05. When specified or as directed by the Engineer, place geotextile prior to placing grout bags/mats. Position the bags and fill them so that they abut tightly to each other and to the substructure units. Stagger joints between bags in successive rows and tiers. Position mats and fill them so that they abut and seal tightly to the substructure. Prevent and eliminate open gaps. Use a concrete/grout pump that is capable of delivering up to 25 yd3/hr. Grout bags may be used to seal off voids while grout mix is pumped into the voids. If grout bags are used for this purpose, install 4 in. minimum diameter vent pipes at 4 ft maximum spacings to allow all trapped water in the void to escape while the grout is being pumped. Insert the concrete/grout tube delivering the mix to the void so that the mix does not free fall. Fill the void by the tremie method. Remove the vent pipes or cut off flush with the bags when completed.
476.04 Measurement and Payment
The payment will be full compensation for bags, mats, geotextile, excavation, dewatering basin, hauling, disposal, vent tubes, and all materials, labor, equipment, tools, and incidentals necessary to complete the work.
476.04.01 Grout bags, grout mats, and grout for filling the bags, mats, and undermined areas will be
measured and paid for at the Contract unit price per cubic yard for either Grout/Grout Bags for Scour Protection or Grout/Grout Mats for Scour Protection, whichever is specified.
476.04.02 When grout bags or grout mats are not used to seal voids, the grout will be measured and
paid for at the Contract unit price per cubic yard for Grout for Undermined Areas.
476.04.03 When not specified for reuse of suitable dredge material, election to recover, dry, stockpile,
and reuse suitable dredge material shall be at no additional cost to the Administration.
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