By lyndamyer
The micro TBM, which was installing a 900mm diameter storm sewer and was commissioned in March last year, had stuck on Toronto’s Basement Flooding Protection Program and after 15 months has been retrieved.
While in June 2022 during steel tie-backs used for brace shoring for two mid-rise developments in the area, this TBM became stuck, in order to retrieving it and the City of Toronto issued an emergency contract to Clearwater Construction Ltd in March 2023 and the scheduled date for completion of the operation is early April.
According to a spokesperson for the city’s Engineering and Construction Services division: “The retrieval was a complex operation, requiring more time and cost than initially anticipated. During initial retrieval efforts, a significant amount of groundwater entered the tunnel, which needed to be removed and the ground needed to be stabilized in order to safely continue work and remove the machine. The ground stabilization work was more complex than originally anticipated, however, the area always remained safe.”
While the first purchase order for the retrieval was for C$8.99m (£5.4m), following the efforts to retrieve the machine advanced, the city amended the purchase order for an additional allocation of up to C$16m (£9.6m).
“This represents the upper limit of the cost estimate, and it’s possible that the cost won’t require the entire amount. The final costs and actual payments will be based on substantiated and certified invoices,” added the spokesperson.
With the determined completion date by the end of the year, work is going to resume on the new sewer and work on the Old Mill Drive, whereas the TBM had completed 95% – 275m – of its drive when it hit the tiebacks. The location of operation of this 1.2m diameter, 5m-long machine was at a depth of 6-18m for avoiding conflict with the nearby Old Mill TTC Subway tunnel.
Considering that leaving this machine in the ground would have required the sewer to be completely redesigned and reconstructed which would have been cost-prohibitive and extended the Basement Flooding Protection Program project’s duration, the City of Toronto decided to retrieve it.
