A Case Study for Characterizing Undrained Cyclic Deformation Properties in Young Sand Deposit from In-Situ and Laboratory Tests

Abstract

This paper describes a case study in which undrained cyclic deformation properties of a recent sand deposit in use for seismic response analysis was investigated through a comprehensive site investigation, coupled with cyclic loading tests in the laboratory. The test site comprised a loose sand deposit in Tokyo Bay which was reclaimed in 1960'. The objective of this investigation was to examine the applicability of profiling small-strain shear modulus and damping characteristics of the recently reclaimed sand deposit by performing undrained cyclic triaxial and / or torsional shear tests on disturbed sand samples retrieved by ordinary tube samplers, and also on fully reconstituted samples prepared with a void ratio similar to the in-situ subsoil. Two types of sand sample with high and low quality were obtained by means of in-situ ground freezing technique and by ordinary tube samplers, respectively. The quality of the samples was evaluated by comparing the pseudo-elastic shear modulus, Gmax, from the laboratory cyclic loading tests to Gf from an in-situ downhole seismic cone test, which was involved with little disturbance to the original subsoil. On the basis of the test results, it was concluded that for this loose sand deposited only thirty years ago, the aging and structural effects were not significant with respect to the undrained cyclic deformation properties at small strains. It was also demonstrated that the undrained cyclic deformation properties can be evaluated with laboratory tests on isotropically consolidated specimens using disturbed or even fully reconstituted samples when the density profile with depth is pre-determined by means of appropriate in-situ tests.