The City of Toronto is spending $9 million to rescue a micro-tunneling boring machine that became ensnared by steel wires nine months ago while constructing a new storm sewer.
The emergency safety measure will be undertaken by Clearway Construction Limited later this month as a matter of “extreme urgency,” states a city report, which notes that public safety is a concern due to ground instability and sinkholes.
City officials say that the steel tiebacks that entangled the machine were part of a deep foundation shoring system used for the construction of adjacent mid-rise buildings.
“As the work progressed, the contractor encountered a significant increase in groundwater infiltration into the recovery tunnel at the face of the micro-tunneling boring machine, which caused increased ground movement around the machine, resulting in a sinkhole in the work zone,” the city report states.
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Clearway’s efforts will not be the first time that the boring machine has needed to be rescued. The machine, activated under the city’s Basement Flooding Protection Program, encountered a vertical alignment issue in 2022. After being trapped for nearly four months, Earth Boring Co. Limited removed its machine by building a rescue shaft in spring 2022.
Just one month later, in June, the machine became trapped again, this time due to its entanglement in the wires under Old Mill Drive.
The city brought in an expert in ground improvements and stabilization to assist with implementing an approach to stabilize the soil around the boring machine.
Work to prepare for the machine’s removal continued into 2023. In January, a contractor completed injection grouting for 51 holes to stabilize the ground.
Recently, Clearway has performed jet grouting, vacuum excavation and the installation of PVC sleeves that will assist in preparations for the rescue.
Completion of the remaining section of the recovery tunnel along with the removal of the boring machine is expected to require two to four weeks with completion targeted by the end of March.