City spending $9M to rescue micro-tunneling boring machine stuck underground near Humber River
Face of the micro-tunnelling boring machine entangled in a steel tieback. (City of Toronto)
Published Saturday, March 4, 2023 5:06PM EST
Last Updated Saturday, March 4, 2023 5:06PM EST
The City of Toronto has issued an emergency contract to a construction company to retrieve a boring machine that’s been stuck underground in the west end for nine months after it became tangled in steel wires.
The contract, awarded to Clearway Construction Ltd. last month, is valued at just under $9 million and is “a matter of extreme urgency, as there was a significant health and safety hazard to the public,” according to the city.
Since June of last year, the tunneling machine has been stuck underneath Old Mill Drive, near Bloor Street West, where its presence has caused a number of problems for surrounding infrastructure over the past few months.
The machine was first put into the ground in March 2022 to dig a 900 millimetre diameter storm sewer along Old Mill Drive north of Bloor Street West as part of the city’s Basement Flooding Protection Program.
The sewer is meant to divert rainfall away from homes in the area and decrease the risk of basement and home flooding.
While the machine stayed on course for most of its journey, it encountered an issue in May that caused it to deviate from its path, requiring it to be rescued and realigned.
But less then a month later, the machine’s front cutting end became ensnared in steel ‘tiebacks’ – buried wires previously used to brace shoring from two mid-rise development excavations in the area.
The machine was stopped in its tracks and the tangled mess once again required a rescue effort, as it posed a serious threat to surrounding infrastructure both below and above ground.
“The integrity of the roadway, nearby subway tunnel and surrounding infrastructure was undermined as a result of ground movement around the micro-tunnelling boring machine due to excessive ground water and poor soil conditions,” the city said in a February report.
“This ground instability further led to the creation of a sinkhole in the work zone.”
The city says it looked at a number of options to address the situation, one of which was a “full abandonment” of the machine, which would have cost an additional $5 million, according to city estimates.
Ultimately, it was decided that a ground stabilization firm would be brought in to shore up the soil around the machine so crews could dig into the ground, remove the tiebacks and rescue it – piece by piece.
The ground stabilization work was completed in January and February of this year, with rescue efforts soon to get underway.
Fortunately, the storm sewer the machine was initially tasked with digging was almost completed by the time it got stuck, so it will be finished eventually.
As for the boring machine, the city’s February report said it expects it to be fully removed by the end of this month.