“The City of Toronto has issued an emergency contract to retrieve a boring machine that has been stuck underneath Old Mill Drive, near Bloor Street West, where its presence has caused several problems for surrounding infrastructure over a 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 integrity of the roadway, nearby subway tunnel and surrounding infrastructure were undermined as a result of ground movement around the micro-tunnelling boring machine due to excessive ground water and poor soil conditions, this ground instability further led to the creation of a sinkhole in the working zone.”1
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.
Keller Foundation was retained to perform compaction grouting operation within the disturbed profile to fill voids and stabilize and densify the in situ soils. As a secondary benefit, it will provide a safe working platform for the jet-grouting operation.
In the fall of 2022, GKM Consultants was mandated to provide and install geotechnical instruments to monitor ground, existing utilities, and shaft movements during and after the stabilization process and jet grouting.
To measure ground and utility displacement, we installed a total of 5 SMPs and 3 UMPs. Two inclinometers were also installed to measure lateral displacement of the shaft. The installation and baseline were conducted prior to commencing the grouting operation. And routine monitoring is performed daily to record any movement or settlement during the operation.
The project also aims to meticulously monitor vibrations in residential areas, ensuring comprehensive data collection for both present assessments and future reference. Specifically, it focuses on vibrations generated by open-cut excavations within these communities. By implementing robust monitoring systems, the project seeks to safeguard the well-being of residents while also establishing a valuable repository of vibration records for potential future developments and regulatory purposes. Through diligent observation and analysis, the project endeavors to strike a balance between developmental activities and the preservation of residential tranquility. Two units are currently installed in the Old Mill Drive area and are monitoring the vibrations.
Utilizing our knowledge, expertise and having experienced staff on the field, GKM Consultants is pleased to have helped our client achieve their monitoring goals.
1-CP24 Report Published Saturday, March 4, 2023, 5:06 PM EST
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