Volume 36 (1996) Issue 2 Pages 57-68
Sample quality was studied at two different sites in Japan where thick marine holocene clay is deposited. Six different types of samplers used in this study were : the Japanese standard thin wall samplers with and without piston, the Laval sampler, the Shelby tube, NGI 54 mm and ELE 100 mm piston (ELE100) samplers. Sample quality was evaluated by the unconfined compression test, which is a standard test for evaluating undrained shear strength in Japan. It was found from this comparative study that the sample quality obtained by the Japanese piston sampler is the same as that obtained by the Laval sampler. The Shelby tube and the ELE 100 sampler, however, both provided poor quality samples. It is important in practice to establish a method for evaluating shear strength of soft soils without being affected by sample quality. Three types of laboratory tests were performed to evaluate the influence of sample disturbance on undrained shear strength : laboratory vane test and recompression techniques using triaxial and direct shear testing equipment. It was observed that these methods are quite useful to evaluate shear strength even for poor quality samples.