JACKING OF LARGE UNDERPASSES - A NEW BRIDGE CONSTRUCTION MARKET?

There are very few new bridges to be constructed in Sweden. A new market may be created by the fact that Swedish railways are introducing high speed trains on trunk routes, and this necessitates grade separated junctions. However, the conventional method of constructing underpasses by diverting rail traffic is unacceptable. Jacking of underpasses is now an economical method. An underpass 24.6 M long, 13 M wide and of 6 M overall depth was recently jacked underneath a rail crossing comprising 4 tracks and three sets of points. It was stipulated that rail traffic must not be disturbed and that no movement must occur in the tracks. The underpass weighing 2500 tons was cast in a Pit to the south of the railway line and was then jacked through the sandy soil. The required jacking force was 2600 tons, but the jacks and abutments were designed for a jacking force of 4000 tons. Eight hydraulic jacks, each of 1500 ton rating, were used. Standard materials were largely used for the temporary bridge structure. Large excavators were used to remove soil through the underpass. The cost of the underpass including jacking was kr 3.6 M. The total project cost including road construction was skr 6.1 M.