Toronto searching for cost-effective options to recover tunnel boring machine

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Michael Lewis

Special to Ontario Construction Report

Toronto is searching for cost recovery options after a boring machine digging a tunnel for a storm sewer pipe to alleviate basement flooding in a west end neighborhood became stuck deep underground leading to an additional $16 million expense to extract the equipment and complete the project.

In a July meeting that saw the additional payment to prime contractor Clearway Construction Ltd. unanimously approved by members of the city’s general government committee, Ward 18 (Willowdale) councillor Lily Cheng noted that previous reports said legal staff would seek cost recovery opportunities. She asked for an update on that process and if insurance might cover the expense.

“Obviously, the work is underway,” said city solicitor Cory Lynch. “Legal’s intimately aware of this file now and really engaged in it and exploring all issues to come up with a proper opinion for the committee and council at the appropriate time.”

Committee chair, Ward 6 (York Centre) councillor James Pasternak said one of the options would be “to recover funds through litigation.” Clearway did not immediately respond to a request for comment.

toronto councilThe project to dig the 900 millimetre diameter sewer along Old Mill Drive north of Bloor Street West was first budgeted at $7.2 million. The machine was to be placed 18 metres below ground to avoid the nearby Bloor-Danforth subway line and extend 282 metres to a pre-constructed exit shaft on Bloor Street.

The $3 million, 1.5 metre wide and five-metre-long remote-controlled micro-tunnelling boring machine was installed in March of 2022 and became stuck in June of that year. Since then, road closures, construction vehicle traffic, dust, noise and vibration from tunneling work have caused frustration and concern in the community.

In March, the city signed a deal with Clearway to extract the machine for an estimated $9 million. Including taxes, the city says the cost could now surpass $25 million –with the project expected to be completed in August.

Judy Tse, the city’s interim chief engineer, told the committee that the storm sewer boring project was initially a one-month job “but as work progressed it ran into a bit of a problem.” About 7.5 metres away from the exit shaft the boring machine became ensnared in steel wires left underground from nearby condominium foundation work.

The contractor and a consultant decided that handheld tools would be used to dig the remaining tunnel. In the process of the work, Tse said it was discovered that the machine had encountered 14 steel tiebacks in the tunnel and that the hand mining had disturbed ground water that was entering into the sub ground void and creating sink holes.

“That was deemed as an emergency,” she said. The prime contractor was asked to retain a subcontractor to stabilize the ground to allow extraction of the machine and resumption of the project. “In order to safely proceed with the removal of the machine, the water needed to be removed and the surrounding ground area stabilized,” the city said in a statement. “This required an expert in ground improvement and stabilization.”  Tse said a nonnegotiable contract was entered into for the emergency work.

Advised by the contractor and consultant last April of more ground instability and that more time and labour would be needed, she said the city was told that an “additional $16 million would be required to complete the work. Payment would be evaluated and based on our assessment.”

Tse said simply leaving the tunnel machine in place would be the most expensive option. “Attempting to complete the basement flooding protection work around the machine would be cost-prohibitive, as the sewer would need to be re-designed and re-constructed,” the city statement said.

The remaining work to retrieve the machine includes the completion of a recovery tunnel, the installation of 12.5 metres of sewer pipe, as well as repairs to the machine.

The city says the final cost will be made public once all invoices are processed.

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