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The eŠects of sample disturbance on undrained shear strength were investigated from samples with various qualities, retrieved by diŠerent types of samplers at the Takuhoku site, Sapporo. Sample quality was evaluated by three types of shear tests: unconˆned compression, fall cone and triaxial recompression tests. Similar to a previous study conducted by Horng et al. (2010), in which the sample quality was evaluated by two nondestructive tests, the residual eŠective stress (suction) by ceramic disc and the shear modulus by bender element under unconˆned conditions, the present study shows that the small edge angle of a tube sampler is important to obtain high quality sample. In addition, the existence of a piston does not have a signiˆcant eŠect on the strength properties. The recompression technique in the triaxial test, where the specimen is consolidated back to the in situ stresses, was able to duplicate undisturbed soil behavior except when the structure of a soil sample was signiˆcantly destroyed. The unconˆned compressive strength is apparently governed by the residual eŠective stress. From the two types of tests simulating sampling processes, however, it was found that a reduction in the unconˆned compressive strengths of low quality sample was brought by the loss of the residual eŠective stress as well as destruction of soil structures.

Effects of sample disturbance on the undrained shear strength were investigated from samples with various qualities, retrieved by different types of samplers at the Takuhoku site, Sapporo, Japan. Sample disturbance, caused by difference in sampling tube geometry, was evaluated by two nondestructive methods: measurement of residual effective stress (p'r) by ceramic disc; and shear wave velocity (Vs), and thus maximum shear modulus (GBE), by bender element. Sample quality was also evaluated by three types of destructive test, i.e., shear tests: unconfined compression, fall cone and triaxial recompression tests. Geometry effects of the sampling tube, for example, thickness of the tube wall, edge angle, and existence of a piston were carefully examined. It was found from these studies that the small edge angle of a tube sampler is important to obtain high quality sample. In addition, the existence of a piston does not have a significant effect on the strength properties.

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