GRP Sewer Crossing Beneath Railway Installed by Trenchless Pipe Jacking in Great Britain

The initial proposal was to use concrete pipes to replace the existing 980 x 920 mm brick sewer but the additional wall thickness of the concrete pipe and socket, plus the weight of the pipes raised difficulties concerning design and construction: A large and expensive crane would have been required outside the station due to the large lifting radius necessary for the pipes’ weight and size.An alternative using HDPE was considered and could have been sleeved inside the existing sewer each side to make a connection that was quick to establish. However, calculations showed that the fastest solutions are not always the best: the deflections under the rail load would exceed the 3 mm limit set by the railway operator.HOBAS CC-GRP Jacking Pipes are designed to take the high axial loads applied during installation. Their wall structure also makes the pipes very stiff and act more like rigid than the flexible pipes they are designed as. Calculations undertaken by Professor Falter of the University of Applied Science in Münster, Germany, showed that the deflection of the utilized HOBAS Pipes OD 924, SN 64000 with a wall thickness of only 77 mm under railway loads of 140 kN (= 14.3 tons per m²) and at the shallow cover of partly 60 cm was less than 2 mm.