STEEL CAISSON FOR WELL FOUNDATION OF RAIL-CUM-ROAD BRIDGE OVER RIVER BRAHMAPUTRA AT JOGIGHOPA

This paper describes the design and construction of a double-decker bridge across the River Brahmaputra at Jogighopa, Assam, India. The upper deck of the 2.280km long bridge is to connect the NH-31(b) highway on the north bank with the NH-37 highway on the south bank; there is also 1.082km of connecting road viaducts. The lower deck carries a railway line across the river. The bridge has 19 main pier foundations, each of which is a well foundation, and two twin circular well abutments on each side. Two of the foundations are on rock, and use a combination of 18m diameter circular well the 12 1.5m diameter piles anchored into the rock. 17 of the wells are founded on dense sand, and are of 11m x 17m double D-type, using a steel caisson. The paper gives details of the design, fabrication, launching, floating, and grounding of the caissons. It also discusses the problems faced during construction, how they were solved, and what precautions were taken. A complete 12m caisson could be made within about two months. Although construction of the bridge foundations was made more difficult by the unpredictable flooding behaviour of the river, the use of caissons made it possible to tackle successfully all problems arising.