Phase 1 of the 5.5km, $32m Perry Hall to Gravelly Sewer contract in Birmingham, UK, is back on track after a TBM failure earlier this year delayed the contract by several months. The tunnel drives on Phase 1, being undertaken by Amey Construction, are expected to finish at the beginning of this month

In January 1999, the Lovat TBM experienced difficulties with its main bearing, resulting in failure under Gravelly Hill. A rescue shaft was sunk and the main bearing removed for examination. The machine restarted in September this year after repairs had been carried out.

In an attempt to recover lost time and maintain schedule, a second Lovat was sourced from the US, which began tunnelling in June 1999. Excavation is continuing with both machines and good progress rates are reported. The completion date for the whole project is April 2000 and it is on target.

The 5.5km long sewer tunnel has a 3m i.d. and is lined with precast concrete segments. The depth is 6-30m, with 20 shafts ranging from 4m to 9m diameter.

The sewer was divided into two contracts of equal length with each contractor originally using a single Lovat TBM. Phase 1 was awarded to Amey Construction in December 1997, with Phase 2 being awarded shortly afterwards in March 1998 to Murphy & Sons. Phase 2 has already been completed and was driven through shallow mixed face conditions in the river basin. Although ground conditions were problematical and the contract was not without its difficulties, no problems of a scale similar to those on Phase 1 have been reported.

Harry Driffill, senior engineer with STW, said of the project: "Teamwork between STW, Haswell, Amey and Murphy has been a major contributor to the success of the project, enabling the resolution of a difficult situation on Phase 1 and bringing the scheme back on track."

The sewer forms the last link in a system of 40km of sewers begun in 1974, called the Black Country Trunk Sewer. Client for the project is Severn Trent Water, which appointed Haswell Consulting Engineers to finalise the route, start detailed design and supervise construction on the 5.5km sewer tunnel scheme.



Related Files
Map of the Perry Hall to Gravelly Sewer tunnel alignment.