Project Description
In late 1993 difficulties were encountered in the operation of the tunnel boring machine (TBM) during mining for the new rail tunnel to connect Sarnia, Ontario, Canada with Port Huron, Michigan, United States. This necessitated removing and servicing the cutterhead before the TBM continued under the St. Clair River.
deep foundations contractors inc. were selected from a group of North American contractors to construct a shaft large enough to remove the 9.5 metre (31 foot) diameter cutterhead to the surface. This required a 10.0 metre (33 foot) x 3.7 metre (12 foot) hoisting space. The invert of the TBM was 29 metres (95 feet) below grade in very week clays, described as having a tooth-paste-like consistency. This soil was sensitive, losing strength when disturbed or stressed. During construction of the original tunnel, built in 1890, numerous failures had occurred while attempting to excavate shafts in this material.
Deep Foundations installed a series of 227 tangent caissons with diametres of 0.9 metres (3 feet) to 1.2 metres (4 feet) to depths of 33 metres (108 feet). In order to accomplish this installation, we required over 7 kms (about 5 miles) of drilling and created a cylinder of sand and cement about 15 metres (50 feet) in diameter. A rectangular shaft was excavated within this cylinder and was braced internally. The bracing consisted of steel walers and temporary struts. The latter were removed to allow the cutterhead to be hoisted.
Project Details:
Owner
St. Clair River Tunnel Company
– Canadian National Railways
Shaft Engineer
Isherwood Associates Oakville, Ontario
Project Engineer
Hatch, Mott MacDonald
Project Value
$4,500,000 CAD
($4,250,000 USD)