ABSTRACT:

The kinematic nature of small-strain stiffness (i.e., elastic modulus) of a granular soil was investigated by performing segmental triaxial compression tests on specimens of Hostun sand. A pause was allowed after each segment of virgin shearing to allow for creep to occur. When the creep rate decreased to a minimum value, the next segment of shearing (i.e., reloading) by increasing deviator load was applied. Elastic modulus was measured at every onset stress-states of reloading by applying small-amplitude cyclic loading CL. In some occasions stress-state was unloaded to the initial isotropic stress-state, followed by a pause for delayed rebound to occur; the specimen was reloaded to the next predefined stress-state. During this overall unloading and reloading, small-strain axial CL tests at various stress-states were applied to determine the dependency of Young"s modulus on axial stress. It was observed that the initial stiffnesses¾the elastic Young"s modulus, the secant modulus and the tangent modulus¾at every reloading stress-states were similar to each other. Deformation characteristics of each reloading segment was similar to that occurring when a specimen was subjected to triaxial compression after consolidated isotropically or anisotropically at the same stress-state.

INTRODUCTION

The deformation of geomaterials measured at strains smaller than about 0.001% in monotonic loading tests is essentially strain rate-independent and recoverable (Tatsuoka and Kohata, 1995), and the initial stiffness values at very small strains determined by static monotonic loading tests are essentially the same with those determined by the corresponding static and dynamic cyclic loading tests (Jamiolkowski et al., 1991 and Tatsuoka et al., 1994). This indicates that a consolidated specimen may exhibit linear elastic deformation at that small strain level, which is independent of the initial stress state; that is, independent of whether the specimen is consolidated isotropically or aniostropically.

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