An Energy Model Of Dynamic Pore Water Pressure Development For Saturated Loose Sand Under Complex Stress Condition

The buildup and development of pore water pressure under dynamic load is a key factor to the deformation and strength behavior of soils. Therefore the research of pore water pressure is one of the important issue in soil dynamics. It is known to all that stress is a vector. It is difficult to some complicate problems while stress pattern is used to analyze the pore water pressure. Since energy is a scalar, energy approach may be successfully used in solving complex problems which are difficult to solve with the stress method.In practical engineering problems, the initial stress conditions for soil elements beneath the foundation of the building are usually rather complex. In this state, if the foundation subjected to complicated cyclic loading induced by earthquake shaking and ocean wave, the response of pore water pressure will be very complicated. At the present time, the patterns of pore water pressure were often aiming at two-directional consolidation condition and simple circle stress path. The analysis of tests shows the model of pore water pressure under two-directional consolidation is not appropriate to multi-directional anisotropic consolidation. It is necessary to set up the pore water pressure model under complex stress condition.The soil static and dynamic universal triaxial and torsional shear apparatus is facilized by Dalian University of Technology and Seiken Inc. and made by Seiken, Japan. The apparatus is used to perform experimental tests of Fujian loose standard sand subjected to simple cyclic torsional shear and vertical-and-torsional coupling cyclic shear with different shear stress path under isotropic consolidation, and cyclic torsional shear under three-directional anisotropic consolidation condition with different initial consolidation parameters. The influence of cyclic shear stress path, initial deviatoric stress ratio, orientation of initial maximum principal stress and initial coefficient of intermediate principal stress on the relationship between pore water pressure and the accumulate energy dissipation is studied.The program is used to compute the areas surrounded by stress and strain, and accumulated energy dissipation is achieved. Based on the experimental and analytical studies of Fujian loose standard sand, a simple method is used in computing accumulated energy dissipation. By contrast with the accumulated energy dissipation computed by the complicated method, the simple method can reduce the computed error. The simple method is proved to be reasonable and feasible.The experimental results of Fujian loose standard sand show the developments of pore pressure in soils is closely related to accumulated energy dissipated in the soil during the process of vibration. The effect of different cyclic shear stress path under isotropic consolidation on the relationship of pore water pressure and accumulated energy dissipation is very little, itcan be ignored. The orientation of initial maximum principal stress under three-directional anisotropic consolidation has some influence on the relationship of pore water pressure and accumulated energy dissipation, but the effect of initial coefficient of intermediate principal stress is less, whereas the effect of the initial deviatoric stress ratio is larger. The parameters on the initial deviatoric stress ratio and the orientation of initial maximum principal stress are introduced to the results, an energy model of pore water pressure development for Fujian loose standard sand under complex stress condition is elementarily established.The apparatus is also used to perform experimental tests of saturated Nanhai loose calcareous sand subjected to cyclic torsional shear and cyclic circle coupling shear under isotropic consolidation, and cyclic circle coupling shear tests under three-direction anisotropic consolidation with different orientation of initial maximum principal stress and different initial deviatoric stress ratio. The influencing factors on the relationship between pore water pressure and the accumulate energy dissipation of saturated Nan...