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Continuing Rescue Process of Micro Tunnel Boring Machine in Toronto

TBM Stuck in Steel Tiebacks Rescue Process

After a year that it became stuck in steel tiebacks while constructing a new storm sewer in Toronto, the micro tunnel boring machine (TBM) is still under rescue mission.

As part of the City of Toronto’s basement flooding protection program, construction of a new 900mm diameter storm sewer along Old Mill Drive was duty of this machine.

While the responsibility of advancing this work was up to Canadian construction company Clearway Construction Limited on behalf of Toronto City Council, in March 2022 the machine deviated off its alignment. During a hand mining operation for liberating the machine, it was found that the machine was entangled in a steel tieback that is part of a deep foundation shoring system for the construction of mid-rise buildings on the road.

Considering that there was a significant health and safety hazard to the public, the rescue of the machine was a matter of extreme urgency as in previous month it reported by Toronto’s General Government Committee.

Due to the significant increase in groundwater infiltration into the recovery tunnel at the face of the micro TBM, the rescue operations has been faced problems, whereas this caused increased ground movement around the machine that undermined the integrity of the roadway, nearby subway tunnel and surrounding infrastructure. It also resulted in a sinkhole in the work zone.

TBM Rescue Process in Toronto

While, assisting the implementing an approach to stabilize the soil around the machine was up to Keller, WSP Canada has also been advising the city on the rescue project.

In order to helping with the final rescue of the machine, the city council granted a non-competitive contract with CD$9M value to Clearway Construction Limited in February 2023.

The company was brought on board to review the impacted area and safely proceed with the rescue operations, including de-stressing and removing steel tiebacks, and jet and compaction grouting to stabilize the ground.

The estimated date for completion of the remaining section of the recovery tunnel along with removal of the machine is end of this month.

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