New Hampshire’s City of Manchester has awarded the contract for the Cemetery Brook Drain Tunnel project to Methuen Obayashi Joint Venture.
The project aims to transform the city’s drainage system, reduce combined sewer overflows, and improve the water quality of the Merrimack River, a critical natural resource which supplies drinking water for 600,000 residents.
The 3.6km-long bored tunnel will have an internal diameter of 3.65m. It will be built 24m below ground.
Construction will begin on the banks of the Merrimack River where the structures will include a temporary excavation support system, a tunnel launch trench and a headwall.
Seven drop shafts and corresponding structures will be built along the tunnel alignment. The shafts will provide the construction team access to the tunnel and, once the project is completed, they will convey water into the tunnel. The DS-7 shaft will be used to retrieve the TBM.
The shafts will be excavated in in rock either by mechanised excavation or controlled blasting.
Once the tunnel and drop shafts are built, the tunnel inlet at Mammoth Rd, and the permanent outfall structure on the Merrimack River will be constructed.
The US$360m project, undertaken in collaboration with the US Environmental Protection Agency and the New Hampshire Department of Environmental Services, is the largest public works project ever undertaken in the City of Manchester. It is due to be completed in 2028.
