Loading Efficiency and Stiffness of the Lea Park Formation at Borden Bridge

ABSTRACT: The research demonstrates the effect of temporal changes in subsurface pore pressures at the Borden Bridge landslide which are shown to impact the landslide’s rate of movement. A historical perspective of the area shows the failure is being driven along a weakened layer of residual clay shale roughly 40 m below surface. Changing pore pressure dynamics due to seasonal fluctuations influence the modulus and shear strength of the residual clay shale. These changes have the potential to affect the stability and contribute to delayed failure mechanisms for the landslide. Several vibrating wire piezometers and a barologger were recently installed on site. Using the collected dataset, the deformation modulus can be interpreted within the Lea Park Shale. The data presented in this paper includes the stiffness of the residual shale formation below the groundwater level based on historic laboratory results and from in-situ methods.