SMALL STRAIN BEHAVIOUR OF DENSE GRANULAR SOILS BY TRUE TRIAXIAL TESTS

摘要

A series of tests was conducted by using small-scale and large-scale true triaxial apparatuses (where σ_1 ≠ σ_2 ≠ σ_3) in order to study small strain behaviours of dense granular soils including anisotropic deformation characteristics. These apparatuses are equipped with local deformation transducers to measure deformations of prismatic specimens in three orthogonal directions. Dense gravel specimens were prepared by manual compaction and tested in large-scale true triaxial apparatus, while dense sand specimens were prepared by air-pluviation and tested in both scales of true triaxial apparatuses. During isotropic and triaxial compression, at several stress levels, many very small vertical and horizontal cycles were applied to evaluate the quasi-elastic deformation property including Young's modulus and Poisson's ratio at small strain levels around 0.001%. Its inherent and stress-state induced anisotropy could be clearly observed for both cases of dense sand and dense gravel. The inherent anisotropy is affected by the bedding plane or heavy compaction during specimen preparation. The values of Young's moduli in the direction that was perpendicular to the bedding plane are smaller than or equal to those of Young's moduli in other orthogonal directions during isotropic compression for all the tested specimens. Discussions on anisotropic characteristics of dense granular soils including their hypo-elastic modeling are also made.