September 8 saw the breakthrough of the 1.5km long, 2.8m i.d. Walney Island combined storage and transfer tunnel in the UK.
AMEC Tunnelling has completed the $11.2m tunnelling contract for North West Water (NWW) under a design+construct arrangement.
The tunnel is situated along the eastern coastline of Walney Island in Cumbria, north west England, between the Mikasa septic tank and the Mill Lane pumping station, which was constructed as part of the contract. The interior of the pumping station was used as the main drive shaft for the tunnelling works, resulting in the need for all tunnelling work to be completed before internal works on the pumping station could start.
The tunnel was constructed using a 3.3m diameter Lovat RME 131 SE EPB machine named Vicky at a depth to invert of 8m to 16m and an average gradient of 1: 2000. The machine was designed in collaboration with NWW and the Engineer on the project, Bechtel Water Technology, to deal with the locally variable glacial geology. Tight radius curves of 250m were incorporated owing to the profile of the Walney coastline.
The tunnel is lined with trapezoidal rings supplied by C.V. Buchan, an AMEC plc owned company. The rings have a push fit dowel connection on the circle joint which requires fewer bolts and is quicker and cheaper to install.
The works started in November 1998 and have been designed to intercept a number of existing outfalls and overflows to the Walney Channel, so enabling NWW to comply with the EC Urban Wastewater Scheme.
