Sample Disturbance of Onsoy Clay Due to Gas Exsolution

High quality block clay samples at Onsoy were obtained by using the Sherbrooke sampler. Pore water with various degrees of gas dissolved were introduced to soil specimen under a back pressure simulating 1500 m water depth. Then total stresses were released, resulting in gas coming out of solution before trimming samples for advanced tests. Results from both Triaxial compression tests (CAUC) and Direct simple shear tests (DSS) showed that sample disturbance is increasing due to gas exsolution up to eta = 20% and there is less increase in effects on undrained shear strength for eta = 20 to 67%. Delta e/e(i) and anisotropy ratio indicate that sample disturbance due to gas exsolution has more influence on DSS and CRSC tests than on CAUC tests. CRSC tests showed that preconsolidation stress is decreasing with increasing degree of gas saturation. Tube sampling disturbance of onsoy clay from previous study is discussed and compared with disturbance due to gas coming out of solution.