Stiffness Degradation and Sample Damage of the Lea Park Formation Shale for A Slow-Moving Landslide in South-Central Saskatchewan

Abstract

Geotechnical structures built on shales with smectite can result in relatively conservative design or metastable structures. A smecititic shale will be hydrophilic and prone to swelling and degradation upon drilling and sampling. This research demonstrates the use of laboratory and in-situ testing to determine a level of stiffness degradation with sampling methods in a Cretaceous clay shale. The bedrock material of interest for this research is the Lea Park Formation shale. Several sampling methods were employed in this study and are used to gather relatively undisturbed samples of the shale at depth. The stiffness of the recovered samples was then evaluated using both small strain and engineering strain increments. Several in-situ testing methods including surficial and downhole geophysics as well as barometric compensation are used to gather in-situ small strain, and intermediate strain moduli at depth. Laboratory methods are used to gather the larger (engineering) strain modulus of the shale. The data presented in this thesis attempt to show the level of damage in the shale bedrock with drilling, sampling, storage, and test procedure. The stiffness degradation with varied levels of strain are also evaluated. These values are then compared with empirical methods to determine the most accurate methods of predicting stiffness degradation for modeling of strain dependant problems.