Study on deformation and strength characteristics of course grained soils under wide variety of stress and strain states

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In order to investigate and model the mechanical behavior of course grained soils under a variety of stress states with different stress histories, two series of triaxial tests were conducted on rectangular specimen (with cross-section of 23^*23 cm and height of 58 cm) of densely compacted gravel. Based on results from a series of cyclic triaxial tests following different stress paths under several levels of confining stress, a unique relationship between modified stress and strain parameters during monotonic loading was proposed. By combining this relationship with newly modified hysteresis laws, it was demonstrated that the proposed model could reasonably simulate the cyclic behaviors of dense gravel. Based on results from another series of triaxial tests, their creep behaviors were found to be not negligible, with considerable effects of change in the strain rate on the monotonic loading properties.Studies were also made on the elastic wave velocities of sands and gravel. On Toyoura … More sand, primary wave velocities measured with small accelerometers that were set on the side surface of rectangular specimen were found to be consistent with the static Young's moduli evaluated by applying small amplitude cyclic loading. On gravel with larger particle size, however, the wave velocities were much higher than the statically evaluated values, due possibly to the effects of inhomogeneity in the structure of soil particles.In addition, a large scale true-triaxial apparatus equipped with a pair of horizontal loading plates and a medium scale triaxial and torsional shear apparatus equipped with a local deformation measurement system for hollow cylindrical specimen (with outer diamete of 20 cm, inner diameter of 16 cm and height of 30 cm) were newly introduced. Based on results from preliminary tests, their accuracy in controlling and measuring stresses and strains was confirmed.These apparatuses enabled to make comprehensive studies on anisotropy of deformation properties in the vertical and horizontal directions and their changes due to rotation of principal stress direction. Less