SUBMERSIBLE BRIDGES AND SCUPPERS

On beds of sand, loam or clay, a monolithic base construction or a cement concrete raft which runs Continuously over the entire length, with sloped aprons and cut off walls or dwarf walls on both the upstream and downstream sides are provided to guard against the scour and undermining. Boulder pitching encased in wire netting is provided in the bed on both sides away from cut off walls. The abutments are made solid and of massive construction, the approaches which should generally follow the bank slope are also paved solid exceeding 45 cm above highest flood level and made in the form of scuppers with upstream and down stream small dwarf walls and pitching where required. Wheel guards are usually provided on the bridge instead of railing. As for as design parameters are concerned a submersible bridge should have deep foundations much below the scour depth. Openings may be of arches, slabs or pipes. The structure of the bridge should be heavy and massive, and should be safe against overturning or uplift under the critical conditions ie, when the flood water is just about to overtop. Section should be as to have least area of obstruction to the flow of water, should have minimum number of piers and small thickness of the decking, with no parapets. All filling should be such that would stand submergence. Headroom should be so fixed that the bridge would not be closed to traffic for a longer period than the traffic can afford. Spans should also be fixed according to the requirements of the traffic, height of bridge and the flow and the duration of the storm water. Railing shall be either collapsible or removable. For detailed design for a submersible bridge follow IRC-Paper No. 173.