Effects of Sample Disturbance on Dynamic Properties of Sand

Abstract

ABSTRACT Laboratory tests were conducted on sand samples obtained by two different methods: in situ radial freezing which is likely to preserve the in situ dynamic soil properties, and conventional coring with a triple tube sampler. The results show that: (1) despite a relatively small difference in the drained shear strength, the undrained cyclic shear strength of the tube sample is considerably lower than that of the sample by freezing; and (2) the possible cause of this difference is a change in negative dilatancy characteristics due to sampling disturbance. Samples having dynamic characteristics similar to those of the sand by freezing were formed and tests were run on the samples to study major factors influencing sample disturbance. The test results imply that: (1) the shear stress history occurring during sampling is the primary factor reducing the undrained cyclic shear strength and modulus, whereas the reduction of confining pressure alone has negligible influence: (2) the deterioration of undrained cyclic shear strength due to sample disturbance is well correlated with a change in the elastic shear modulus ; and hence (3) the degree of sample disturbance can be assessed to some extent by comparing the two elastic shear moduli measured in the laboratory and the field.