The shales of the Greater Toronto Area (GTA) experience time-dependent deformations (TDD) which are known to be the result of volume change of rock. This change is due to diffusion and dissolution of calcite that is inherent to the shale formation upon introduction to fresh water during excavation and stress relief. These deformations can induce long-term pressures on shaft walls and tunnel linings, especially if the permanent works are constructed soon after excavation with little time delay.
This talk will present measurements of TDD of recent shaft and tunnel projects constructed in the GTA, and draw conclusions regrading the design impacts for engineers and owners.
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