Watermain tunnel under Fraser River finishes ‘within an inch’
September 23, 2015 by STAFF REPORT
What’s been called “the biggest water infrastructure project ever attempted in Metro Vancouver” is under way to build a new watermain under the Fraser River, according to a report in Canadian Consulting Engineer.
The Port Mann Water Supply Tunnel is a $240-million project to replace a 40-year old crossing that was damaged by river scour. The new tunnel is west of the new Port Mann Bridge, 60 metres below the river bed, and 80 metres long.
After almost 17 months of burrowing between Coquitlam and Surrey, the tunnel boring machine “Squirrel” was pulled out of the north shaft this summer.
Work is now proceeding to insert a welded steel water main of 2.1 metres diameter inside the 3.5-m diameter tunnel. Valve chambers are being constructed on top of each 60-metre vertical shaft to allow the system to be connected to the existing Metro Vancouver transmission system by the Fall of 2016.
The tunnelling process took longer than expected due to the underground conditions encountered including difficult ground pressures and mixed soils including tills, clays, “cobbly ground” and boulders. Nonetheless the boring machine hit target within an inch.
McNally International and Aecon Constructors were awarded the contract for Metro Vancouver’s highly challenging Port Mann Tunnel Project at a price of CA$167.3 million.
Designed by the Fraser River Tunnel Group – a joint venture consisting of Sandwell Engineering, Jacobs Associates and Golder Associates – the gasketed pre-cast segmentally lined tunnel will run from North Surrey to Coquitlam through glacial tills and clay deposits at an average depth of 60m (195ft), and 40m below water level under the Fraser River, will ultimately feature a 2.13m (7ft) inside diameter welded steel final liner. Provision for hyperbaric TBM interventions at 6 bar pressure – a first for British Columbia – will be required for the crossing.
The project also includes construction of two 50m-60m (165ft-195ft) deep shafts at either end of the tunnel.
The Port Mann Tunnel is being built as part of Metro Vancouver’s CA$600 million potable water system upgrade that will double supply capacity to areas south of the Fraser River ensuring un-interrupted supply in the event of an earthquake.
Hatch Mott MacDonald is acting as the owner’s project manager.