Construction is underway in Seattle, US, on the starter shaft for a 4.5m diameter Lovat EPBM that is scheduled to start boring a 1km long combined sewer overflow tunnel in March. The refurbished machine will construct the tunnel as part of a new US$42M project in the Rainer Beach district of the US West Coast city of Seattle.
It will be built beneath 42nd Avenue over a period of 16 months at depths ranging from 3m to 9m. The combined rainfall and sewerage will be diverted into either the Renton or King County treatment plants.
The 50-year old existing sewer system suffers 15-30 combined sewer overflows annually. Heavy rainfall overloads the sewer network and untreated sewerage gets washed into nearby Lake Washington.
A joint venture between Northwest Boring and Kenny Construction will be operating the Lovat TBM which has seen similar action in the region, as the client, King County, strives to meet federal targets for waste water treatment.
Main contractor Tri-State Construction of Bellevue will also insert two outlet regulators at each end of the main tunnel, while several 1m-2m diameter microtunnels will connect the main sewer to the open-trench pipeline network. In sections where the pipeline is more than 6m deep, microtunnelling will be undertaken by remote-control at the same time as work on the open-trench pipeline network.
The scheme should be complete by March 2005.
