Canadian Consulting Engineer

Rescue shaft close to trapped tunnel boring machine in Big Pipe

February 5, 2009
By Canadian Consulting Engineer

Tomislav Hrkac, P.Eng., a senior project manager of capital planning for the Region of York, says a trapped tunnel ...

Tomislav Hrkac, P.Eng., a senior project manager of capital planning for the Region of York, says a trapped tunnel boring machine on the “Big Pipe” sewer project north of Toronto should be extricated in a couple of months.

The TBM has been trapped 22 metres underground since May 2008 when the ground above collapsed and 1,800 cubic metres of mud and sand filled a section of the new pipe. The pipe lies below a local aquifer.

The collapse occurred on Langstaff Road in the Richmond Hill area of Vaughan, north of Highway 407.  In order not to hold up the work, a second tunnel boring machine was launched two months later to start working its way west towards the cave-in.

Meanwhile McNally/Aecon, the design-builders, have had to excavate a vertical shaft to reach the trapped machine in order to lift it out with cranes.  By the end of January the new shaft had almost reached the TBM.


The “Big Pipe” project is formally known as the York Durham Sewage System (YDSS) and is part of a huge expansion to the system that feeds sewage from the two regions into the Duffin Creek Water Treatment Plant near Pickering. The tunnel boring machines were working on the 4-kilometre Interceptor Sewer component of the system in York region. Tunnelling was chosen as an environmental alternative for the construction to avoid dewatering which was a concern to local residents.

Hrkac says that they expert McNally/Aecon as design-builders to pick up the cost of retrieving the TBM.

The Big Pipe project has had its fair share of controversy and public opposition. It hit another public relations roadblock recently. Residents in Pickering have protesting against a new odour-control facility that is to be built along the system near Altona Road and Finch Avenue East. They don’t believe the engineers’ assurance that the biofilter technology and charcoal filters will control the odours. An environmental assessment has been filed for the project, with construction scheduled to begin next year.



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