Sample Disturbance Effects on Undrained Shear Strengths—Study from Takuhoku Site, Sapporo—

Abstract

The effects of sample disturbance on undrained shear strength were investigated from samples with various qualities, retrieved by different types of samplers at the Takuhoku site, Sapporo. Sample quality was evaluated by three types of shear tests: unconfined 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 effective stress (suction) by ceramic disc and the shear modulus by bender element under unconfined 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 significant effect 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 significantly destroyed. The unconfined compressive strength is apparently governed by the residual effective stress. From the two types of tests simulating sampling processes, however, it was found that a reduction in the unconfined compressive strengths of low quality sample was brought by the loss of the residual effective stress as well as destruction of soil structures.