ABSTRACT
Swelling may result in excessive pressure and deformation of support system of tunnels if it is not properly investigated by testing and not accounted for in construction and support design. The Georgian Bay and Queenston Shales in Southern Ontario have been reported to have potential for swelling behavior. Swelling is driven by osmosis and diffusion processes that are originated from an outward salt concentration gradient from the rock pore fluid to the ambient fluid. It is known that even when the outward salinity difference exists and water is accessible, swelling does not occur unless the confining stresses applied to a volume of shale is below the suppression stress threshold. It is also known that swelling rate decreases over time, and therefore the maximum swelling is expected to occur in the early days and months after swelling initiation rather than in years, but still swelling strain can increase to several times of the 1-year swelling strain over the lifetime of tunnelling projects. Various constitutive models have been proposed and used in numerical codes to capture time- and confinement- dependency of swelling. In this paper, these models are briefly reviewed and different aspects of design of tunnelling projects in Southern Ontario shale formations are discussed with a few examples of recent and old projects.
