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Cost to rescue micro-tunnelling boring machine skyrockets to $25M

Angela Gismondi
Cost to rescue micro-tunnelling boring machine skyrockets to $25M
CITY OF TORONTO—A City of Toronto report depicts a micro-tunnelling boring machine entangled in a steel tieback in a tunnel on Old Mill Drive.

The cost to remove a micro-tunnelling boring machine (MTBM), which has been stuck under Old Mill Drive in Toronto, has nearly tripled from $9 million to $25 million amid complications.

A request to amend the purchase order with Clearway Construction Incorporate for construction services to remove the machine will be considered at a City of Toronto’s General Government Committee meeting this week.

“The purchase order amendment is required as several challenges were encountered during the ground stabilization works causing the emergency retrieval of the micro-tunnelling boring machine to become more complicated and take longer than originally anticipated,” states a city report.

“Some of the challenges included additional groundwater infiltration and the need for additional ground stabilization work, resulting in the retrieval taking approximately six months longer than initially anticipated, which consequently increased the cost of the project.”

In April 2022, the $3 million MTBM was being used to construct a new 900-millimetre-diameter stormsewer along Old Mill Drive as part of the Basement Flooding Protection Program when it became entangled in steel tiebacks underground which were leftover from the building of a condo development.

At the time the machine got stuck, the tunnelling was about 95 per cent complete and seven metres from its destination.

In 2022, the original cost estimate for the emergency work to retrieve the machine was around $8.9 million, based on the best estimate of the scope of work and costs at the time, indicates the statement from the city.

The extent of the emergency retrieval work became clearer in the spring of this year and staff determined the cost may increase up to an additional $16 million. That could bring the cost of the retrieval project to $25 million.

“City staff and our contractor are working hard to complete this retrieval quickly and safely,” said Judy Tse, interim chief engineer and executive director of engineering and construction services with City of Toronto, in a statement to the Daily Commercial News.

“We are working to remove the micro-tunnelling boring machine by this August, after which we will complete the installation of the new 900-millimetre stormsewer to help protect the area from basement flooding.”

The emergency retrieval process involved hand mining a tunnel from a shaft towards the MTBM, which would then be used to remove the machine.

“During the hand mining, groundwater was encountered, and then when the face of the machine was reached, substantially more groundwater entered the tunnel,” the statement reads.

“In order to safely proceed with the removal of the machine, the water needed to be removed and the surrounding ground area stabilized. This required an expert in ground improvement and stabilization. While the ground stabilization work was more complex than originally anticipated, the area remained safe and stable at all times.”

The purchase order amendment is based on cost estimates and represents the possible costs required to complete the emergency work.

“The final costs and actual payments will be based on substantiated and certified invoices,” indicates the statement.

“The additional funds will cover a number of items related to the increased complexity and extended duration of the project, including labour, equipment and increased restoration costs for the impacted sewers as well as the roads and sidewalks adjacent to the retrieval work zone.”

The city also said there is no working around the machine.

“Attempting to complete the basement flooding protection work around the machine would be cost-prohibitive, as the sewer would need to be redesigned and reconstructed.”

If the retrieval goes as planned by August, the Basement Flooding Protection Program is anticipated to be completed this fall.

Follow the author on Twitter @DCN_Angela.

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