(RE: Island Airport ped tunnel): “It’s not a long tunnel,” concedes Gary Benner, Vice-president of Newmarket-based Technicore Underground Inc., the prime contractor on the project, “but it’s complicated because it’s in shale, not hard rock. That has a big impact on how you build it.”
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As Benner explains, the tunnel passes through soft, horizontally layered shale that is prone to collapsing. Before they could begin to excavate the tunnel, they had to create an arched crown, or secant wall above it in order to distribute the loads and eliminate the possibility of a collapse. They used two laser-guided, manually operated tunnel boring machines (TBMs), nicknamed Chip and Dale, designed and manufactured by a Technicore affiliate.[...]