_GENERAL DOCUMENTS - C1981017 (300)

Home Browse Search

Q 6. LOW WATER CROSSING 6.1 SCOPE- This specification covers all work required for furnishing, hauling and placing materials and constructing the low water crossing specified in the "Invitation and Bid", at the locations and to the lines and grades shown on the drawings or as directed by the PROJECT MANAGER. Please refer to the drawing detail entitled Drainage Crossing. 6.2 DESCRIPTION- The low water crossing shall be constructed across the access road just west of the East Coal Flat to allow drainage to flow west across the road. Prior to constructing this low water crossing, the roadway may require some grading in each direction to establish the final road grade as specified by the PROJECT MANAGER. Bedding All earth material serving as a base for the low water crossing must be compacted to within 90% Proctor density by tamping or rolling prior to - installing a geotextile base. After installing the geotextile below all areas to receive concrete, the CONTRACTOR shall evenly spread a six inch layer of roadbase, followed by the riprap and concrete. The geotextile shall be Mirafi 700x filter fabric (or equivalent) . The filter fabric will be toed-in on all edges the minimum toe-in on the sides is three feet. The slopes on which the fabric is laid shall be graded as smooth as is possible to prevent fabric tears. Hand grading may be required. A single piece of fabric will be used in each area. No splicing will be permitted, unless the sheets are overlapped two feet and double stitched on both ends. Since no bedding is required between the fabric and the rock armoring, riprap must be carefully placed on the fabric to avoid damage. Torn fabric will require patching by double stitching a piece of fabric that extends at least two feet beyond the edges of the tear in all directions. Driving Surface The low water crossing consists of a poured driving surface and poured aprons on the upstream and downstream sides. The CONTRACTOR shall place 18 inches of riprap evenly over the geotextile and roadbase. The CONTRACTOR shall smooth the driving surface of the riprap such that no riprap will extend above the poured concrete. The CONTRACTOR shall pour 2500 psi concrete over and throughout the eighteen inch (18") layer of riprap such that approximately 501", is concrete and 50% is riprap. The poured concrete driving surface shall be forty feet (40' ) wide, twenty feet (20' ) long and eighteen inches (18") thick. The edges of the driving surface shall blend with and match the grade of the existing road surface. The center line of the low water crossing shall be twenty-four inches (24") lower than the edge of the crossing where it joins the existing road surface. The driving surface must uniformly slope towards the center line from its edge to allow for a smooth surface with no sudden or sharp drop offs. -18-