Advances in Design Methodology in Swelling Shale Rock in Southern Ontario

As infrastructure requirements increase in southern Ontario, excavations within swelling rock formations will become more frequent and larger. The objective of this study is to advance design capability for structures in swelling rock through three aspects: i) developing a practical swelling model for design engineers, ii) investigate two crushable/compressible materials for the mitigation of swelling rock effects, and iii) observe and analyze the behaviour of swelling rock to current excavation techniques. A swelling rock constitutive model has been developed. The swelling parameters include the horizontal and vertical free swell potential, threshold stress, and critical stress as well as a “pseudo-Poisson’s ratio” effect that allows the practicing engineer to explore the interaction between orthogonal suppression pressures without the need for advanced testing. The model has been verified through analysis of swell tests and well-documented case studies. Extruded polystyrene foams and light-weight cellular grouts were tested at monotonic low strain rates mimicking the loading behaviour of swelling rock to identify their potential as mitigation materials. Results show low strain rates affect the yield strengths and elastic moduli. Cellular grout test results indicate it behaves as three-phase material in stress and groundwater conditions typical for infrastructure projects. Two case studies were investigated, monitoring, and analyzed. The Zone 1 Water Main project was located in the Halton Region, Ontario and the Billy Bishop Pedestrian Tunnel was located in Toronto, Ontario Results were analyzed to investigate the effect of excavation technique and shape on the elastic and time-dependent deformations of the rock mass