| Summary: | 碩士 === 長榮大學 === 土地管理與開發學系碩士班 === 96 === In this research, isotropic and anisotropic consolidation triaxial undrained test was used to test Mai Liao sand. The mechanical characteristics of the saturated sand were investigated under various initial conditions and stress paths. Under the initial conditions: sand sample with three different relaqtive densities of 40%, 50%, 60%, cyclic undrained shear test was performed. In isotropic case, the initial effective normal stresses were 100, 200, 300kPa. In anisotropic case, the initial values of lateral earth pressure coefficient kc were 0.4, 0.5, 0.67 under various effective lateral and normal stresses.
The results showed that for saturated sand with different relative density the larger the relative density, the higher shear resistance and damage was not easy to occur. When stress ratio was so great that the sand sample failed, phase transformation occurred in both compression and tension sides. Loose sand showed plastic contraction (corresponding to elastic dilatancy), while dense sand shows plastic dilatancy (corresponding to elastic contraction). That is, with different relative density, plastic contraction or dilatancy may occur.
In the beginning of shear test, the pore pressure increased rapidly, and then slowly or even decreased with the increment of shear strain. Therefore, the changes of plastic contraction or dilatancy, and pore pressure depend on relative density of the sand and effective confined pressure.
The results in anisotropic case showed that the mechanical behavior of plastic contraction or dilatancy were the same as that in isotropic case. When the value of kc was changed, the residual stress path always followed the stress path of damage curve. It also showed that with the same relative density and different kc, initial effective lateral stresses did not affect stress path of damage of the sample in both isotropic and anisotropic cases.
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