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Thanks to Southwest Contracting Ltd., there are 16,000 bags of cement buried in North Vancouver. Getting it there was the crux of a major project by the Surrey, B.C. excavation and shoring firm.
The work which recently wrapped up at Vancouver Wharves Ltd. was a contract to Walter Construction (Canada) Ltd.'s sulphur tunnel project on the banks of Burrard Inlet.
Part of the VWL job involved construction of a track and conveyor tunnel into which rail cars will be able to unload sulphur and convey shipments directly to nearby stockpiles or existing shiploaders.
Improvements are expected to accelerate the time it takes to unload a train to four hours from the current 10.
Embarking on the conveyor tunnel, the intent was to excavate and build a concrete tunnel beginning 13 metres below grade and travelling a distance of 77 metres in a gradual rise to grade. Given the waterfront location an obvious obstacle to overcome was the high water table. To prevent both water and earth from caving in around the hole it would be necessary to provide temporary shoring.
The original plan was to drive sheet piles 80 feet down at the deep end on either side then with both sides shored, dredge and dewater the tunnel and do the concrete structure.
Shoring on the west side proceeded as planned, but when it came time to drive the sheet piles on the east side of the tunnel the earth failed to co-operate.
"As Mother Nature would have it we hit some ugly stuff," was how Southwest's excavation and shoring manager Scott MacCara put it.
The sheet piles successfully navigated the first 60 feet down then encountered a layer of...