Written by; Markus MacIntyre / TCCN Staff Writer
Added on: Sun Sep 20 2009
Construction of a new section of a 400 metre section of the 675 mm diameter Moffat Creek sewer line in Cambridge, Ontario is going old-school for the sake of the environment.
Construction workers will use shovels to dig up the earth, and will occasionally use jackhammers to move boulders and recalcitrant till along the line.
Community and regulatory agencies troubled by the effect of open cut excavation to the wetland environment prompted adoption of the labour intensive method of excavation.
The line is an extension of an east-west sanitary trunk in the Moffat Creek Valley. About 4,000 homes are to be built in Cambridge's South East Galt community.
The benefits won't only be environmental, however.
The city will save about $2 million compared to other proposed methods like tunnel boring.
The trenchless technique is like methods used in mining. Rather than open cutting the area, most of the line excavation can be tunneled underground. The route of the affected segment of the sewer runs under several large trees, then wetland. It crosses over top of Moffat Creek proper according to Conestoga-Rovers and Associates, consulting engineers.
First a 1,500 mm diameter steel liner is installed, than the shaft will be excavated to the proper depth of the trunk sewer. A concrete thrust block is then installed at the base of the trunk sewer to begin the tunneling process.
A hydraulic power unit will provide the thrust required to push the tunnel liner through the ground. As the liner sections are put in place, internal laser will provide guidance, and excavated material will be moved away in track-mounted cars.
The whole project is going to be challenging, not only for the presence of the wetland. The other end of the sewer is near several homes. A 50 metre long support wall was constructed near Dundas Street to protect several homes' backyards overlooking the trench site. The project has two 10-person crews working concurrently on different sections.
Copyright: 2009 TCCN.ca