High-Pressure Pressuremeter Tests in the Shaftesbury Shales at the Site C Project

September 26, 2024

Major structures of the Site C Hydroelectric Project are founded in the Shaftesbury Shale. Ménard pressuremeter and plate load testing for those foundations was carried out in the 1980s near a prominent bedding plane at El. 415 m to establish the shale stiffness. The redesign of the Powerhouse and Spillway on a Roller Compacted Concrete (RCC) foundation in 2010 deepened the excavations to El. 375 m to improve the foundation stiffness. Sample disturbance and the presence of pre-sheared bedding planes challenged stiffness determination using conventional laboratory testing. A Cambridge Insitu High-Pressure Dilatometer (HPD) pressuremeter tool was deployed to establish the stiffness of the shale foundation from El. 400 to 340 m. A total of 64 tests were carried out in the shale in 8 boreholes. As expected, the pressuremeter results demonstrated that the deformation modulus was significantly greater than the original design values at higher elevations. This paper focuses on the measurement methodology and the modulus values selected to establish the in-situ deformation profile from El. 400 to 340 m

Dreger, C., D. Martin, Y. Byrne, G. Stevenson, D. Senft, D. Elwood and A. Watson. 2024. “High-Pressure Pressuremeter Tests in the Shaftesbury Shales at the Site C Project,” in Proceedings of GeoMontreal 2024. Resilient Geosciences for Future Generations, 15-18 September 2024, Montreal, QC.