MINED TUNNELING | TECHNICAL


Above, figure 7: Completed Gallery 1A


Rebar Dowels As per design, 15M rebar dowels at a spacing of 275mm had to be drilled into the TTC box before applying the second layer of shotcrete to provide a structural connection between the shotcrete lining and the TTC subway box. Prior to dowel drilling, the contractor had to scan the box base slab for embedded conduits or reinforcement, which proved to be difficult due to the uneven surface of the exposed concrete base slab.


Existing Drainage Pipe / Manhole According to as-built information of the TTC box, an abandoned drainage manhole and a drainage pipe were located underneath the Eastbound box. The exact location was not known and was identified during


the excavation works. The manhole was encountered between Gallery 1B and Gallery 4 and the drainage pipe itself was running in the north-south direction. Special attention was paid when removing the drainage pipe, since the pipe’s material contained asbestos. The asbestos was tested ahead of the construction start and identified as Type 1 (low risk). Nevertheless, once the drainage pipe was exposed, a separate firm specialized in handling and removing construction material containing asbestos carried out the removal in a safe manner.


Monitoring The entire live operating TTC Spadina subway tunnel and the mined galleries were continuously monitored during all tunnel construction activities.


Above, figure 8: Left - Widening of Gallery 1A (Extended Gallery 1A); Right – completed Extended Gallery 1A Winter 2023 | 17


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