TUNNELLING TO complete Yorkshire Water's £70M Humbercare sewerage tunnel in Hull is set to restart next month,18 months after part of it collapsed trapping a tunnel boring machine.
Last month miners broke through to Maureen, the Lovat TBM which was abandoned in November 1999 when water and silt burst into an access shaft and a 150m long section of tunnel causing 2m of surface settlement in a 50m wide trough under a car park.
Tidal effects on a 40m thick layer of soft peat 18m below the tunnel drive are thought to have caused the ground to move around the tunnel, resulting in fatigue failure of the non-bolted segmental concrete lining (Ground Engineering September 2000).
Contractor Miller was forced to pressurise and then flood part of the tunnel.Ground freezing using liquid nitrogen was used to stabilise the ground to allow hand excavation of the collapsed section.
Re-excavation of a 30m section blocking access to the TBM has now finished, allowing engineers to assess damage to the machine. It is believed that the only problems will be electrical, and a portable generator will be used to ensure that the machine is back in operation by May 8.
The TBM will then take five days to drive the 50m needed to complete the works, putting the £200M project on course for completion this summer.