TECHNICAL | MINED TUNNELING
Right, figure 9:
Underpinned TTC Subway Box. The pink color of the steel truss was part of a breast cancer awareness fundraiser
IMAGE COURTESY OF METROLINX
Optical monitoring targets were installed in the
gallery sidewalls, six in total within each gallery. The red trigger level was 8mm inward displacement. The readings in all the targets indicated a stable condition during the entire gallery construction period with maximum recorded displacements in the range of 2mm. Additional to the in-tunnel monitoring, the entire
TTC tunnel, including the rail tracks, were monitored in real-time. Inside the tunnel, electric level beams and tiltmeters were installed. Additionally, the contractor installed Building Monitoring Points (BMPs) outside the TTC tunnel box to monitor the exterior walls/roof of the TTC box. The differential settlement readings of the rail tracks
within the relevant monitoring tunnel box units (underpinning zone) ranged between 0mm and 2mm throughout the construction of the galleries. The alert
level of 3mm was breached twice on one single instrument inside the TTC subway tunnel but the reading was discarded as a false reading due to temperature fluctuation. No action response by TTC and the contractor was required.
CONCLUSIONS A novel underpinning solution of the operational TTC Eglinton West station for the construction of ECLRT Cedarvale station was undertaken utilizing a series of small, mined galleries. These galleries provided access to install a supporting system of steel (needle) beams. The main challenges were the confined space and the tight differential displacement criteria of the TTC box. The construction of the mined galleries was completed in just over two months. The impact of the works on the operational subway was negligible.
Right, figure 10:
Grouting preparation and finalized grout bags
18 | Winter 2023
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