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SUMMARYThis study attempted to investigate the fabric evolution in K 0 loading/unloading. The work made use of a field simulator to control K 0 loading/unloading in large specimens prepared by air-pluviation. In each loading stage, wave velocities along various propagation directions were measured. On the basis of the theories of micro-mechanics and wave propagation, the microscopic parameters of the granular assembly were back calculated to investigate the fabric evolution of granular soil during K 0 loading/unloading.In this study, the Geometric fabric was modelled by fabric tensors of ranks 2 and 4. The comparison of calibrated results using ranks 2 and 4 revealed the advantage of the usage of rank-4 fabric tensor in modelling fabric evolution in spite of its complexity.By comparing relative magnitudes of vertical and horizontal components of geometric fabric, it was demonstrated that relative constraint in lateral directions increased during K 0 -unloading in order to maintain a K 0 condition. It revealed that fabric evolution was responsible for a higher K 0 in unloading than K 0 in loading.

SUMMARYThis study aims to explore the possibility for estimating K 0 in a level ground of granular soil by seismic methods on the basis of micromechanics theory. The idea was to simulate in situ cross-hole seismic method for the measurement of wave velocities along various directions of wave-propagation. This work made use of a field simulator to control a K 0 condition (zero lateral strain condition) in specimens. A series of vertical loading containing subsequent loading and unloading were applied to the specimen prepared by pluviation. In general, the K 0 values determined experimentally in this work agreed with the exiting empirical relations. K 0 value was also calibrated from measured anisotropic wave velocities using an optimization procedure. From the comparison of the back-calculated and measured results of K 0 ; it revealed the feasibility for the determination of the in situ lateral stress in granular soil by seismic methods and on the basis of micromechanics theory as long as enough wave-velocity measurements along various directions of wavepropagation were available. The potential for the usage of the presented methodology for the determination of the in situ lateral stress in level-ground of granular soil by seismic methods seems encouraging.