The City of Toronto appears to be out many millions of dollars as work continues to recover a tunnel boring machine that became stuck under a west end street last year. The five metre long micro-tunneling machine became stuck in April 2022 during construction work to dig a new storm drain under Old Mill Drive
The City of Toronto appears to be out many millions of dollars as work continues to recover a tunnel boring machine that became stuck under a west end street last year.
The five metre long micro-tunneling machine became stuck in April 2022 during construction work to dig a new storm drain under Old Mill Drive near Bloor Street West.
A report from city staff suggests the cost to retrieve the machine has now tripled to $25 million.
“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,” reads the report.
The retrieval of the machinery has taken six months longer than initially planned, which has attributed to the soaring cost of the project. The Purchase Order Amendment request from the city increases the total cost by approximately $16 million, bringing the initial cost of $9 million to around $25 million.
The work on the new storm drain began in March 2022 with the aim of of addressing basement flooding issues in the area. The boring machine was placed deep underground in order to avoid the nearby Line 2 subway.
City of Toronto: scope of work included crossing Toronto Transit Commission’s Line 2 subway tunnel just north of maintenance hole OD8. The Contractor retained a micro-tunnelling subcontractor, Earth Boring CO Limited, to complete the micro-tunnelling work
“In April 2022, the micro-tunnelling boring machine encountered a vertical alignment issue, which caused it to deviate from its alignment of about 7.5 metres from the OD8 retrieval shaft,” reads the city’s report. “This caused the machine to become stuck, requiring it to be retrieved.”
The city hired a contractor to help retrieve the machine, and in May 2022 it was discovered the boring machine had become ensnared in underground steel tiebacks that were part of the construction of nearby mid-rise condominiums.
When the contractor was finally able to reach the machine, they then “encountered a significant increase in groundwater infiltration into the recovery tunnel, which required an expert in ground improvements and stabilization to implement an approach to stabilize the soil around the micro-tunnelling boring machine and allow for its safe recovery.”
A report will be headed to the city’s general government committee next week to explore what’s gone wrong.