Cadent Gas employed the services of Fastflow Energy Services (FES) to install gas pipeline crossings under the M42/M6 Toll motorways, the River Tame and a section of Network Rail ‘live’ track.Trenchless solution specialists HB Tunnelling Ltd were engaged by FES to undertake the package of micro tunnelling works; HB Tunnelling’s appointed engineering design consultant VEDA Associates managed the interface between all parties including Highways England and Network Rail. With all parties having consulted on the options for the pipeline crossings, it was determined that the precast concrete pipe jack method provided the optimum solution with ground conditions being particularly challenging.Prior to the commencement of micro tunnelling on the road, rail and river crossings a number of Tunnel Boring Machine (TBM) launch and reception shafts at varying depths needed to be constructed. FP McCann’s precast concrete segmental shaft rings were the chosen system and due to the soft ground, the caisson method of shaft construction was utilised.
In total six 10.5 metre id launch shafts have been constructed. The TBM reception shafts consist of 1nr 7.5m id, 4nr 6.0m id, plus a smaller 5.0m id shaft. In each case, the caisson ‘jack down’ method was adopted with a 2.0 metre wide by 1.0 metre deep reinforced collar installed around each shaft. The collars acted as a guide ring to keep the caisson shaft vertical and help to resist the forces from the hydraulic jacks.
Trenchless crossings over a total length of nearly 1 kilometre consist of 610 metres of 1200mm diameter pipe jack under the roads and rail track and 333 metres of 1500mm diameter pipe jack under the River Tame. FP McCann’s 1200mm and 1500mm id reinforced precast concrete jacking pipes supplied from the Company’s Alnwick factory formed the concrete sleeve ready for the installation of the 610mm diameter seamless carbon steel gas pipeline.
Commenting on the precast concrete shaft build and pipe jack Brian Sharkey Contracts Manager for HB Tunnelling said, “Using this precast segmental ring method to build the TBM launch and reception shafts is an extremely efficient and structurally sound process. Construction is simple and allows for ease of ground excavation. FP McCann’s reinforced precast concrete jacking pipes provide the ideal sleeve to carry the high pressure gas pipeline beneath these significant sections of trunk road, rail and waterway.”
FP McCann’s smoothbore tunnel and shaft segments are all factory fitted with EPDM rubber gaskets which provide an immediate water-tight seal upon construction. Cross segment connections are made by passing a spear bolt through a pocket in one segment and screwing it into a threaded plastic socket in the adjacent segment. Circle joint connections are made using a ‘T’ bolt passing through a hole in one segment into a ‘T’ box in the adjacent segment. Bolts are designed to fully compress the gasket. Precast concrete jacking pipe is available in sizes from 450mm to 2400mm in diameter. All have self-lubricating joint gasket.