Under an emergency contract, which has been awarded by the City of Toronto, retrieval of a micro TBM that has been stuck underground for nine months after it became tangled in steel wires, is undergoing.
The Intended contract with C$9m (US$6.6m) value, has been granted to Clearwater Construction Ltd, while it is a matter of extreme urgency, as there was a significant health and safety hazard to the public.
March 2022 was the commissioning date of the TBM, that installed a 900mm diameter storm sewer for the Basement Flooding Protection Program Phase 4 Contract on Old Mill Drive, whereas it became stuck in June after being ensnared in steel tie-backs used for brace shoring for two mid-rise developments in the area.
According to Mika Raisanen, director of design and construction, linear underground infrastructure for the City of Toronto division of Engineering & Construction Services: “The tie-backs did not show up on as-built drawings before work began. Processes for tie-back mapping and shoring approvals are now being reviewed.”
Considering that the completed length by this TBM was 95% (275m) of its drive when it hit the obstacles, in order to release the machine and complete the storm sewer work for the project, the remaining 7m section of the tunnel to the shaft at Old Mill Drive and Bloor Street was hand mined.
As well as retrieving the TBM, the remedial works include emergency repairs to the integrity of the subsurface soil to protect the road and surrounding infrastructure, repairing two sinkholes, and removing four tie-backs. The scheduled date for completion of the operation is early April if weather permitting.
The location of TBM’s working is the depth of 6-18m to prevent conflict with the nearby Old Mill TTC Subway tunnel, while this C$3m (US$2.2m) machine is 1.2m in diameter and 5m long.