Experimental study on bidirectional and torsional cyclic loading under different initial stress states in clay

摘要

Before subject to complex cyclic loading induced by seismic loading, the initial stress conditions of soil element beneath the foundation under the structures generally complicated. The principal stresses of soil element under the different locations of structure are usually anisotropic and acted with bidirectional. In order to simulate dynamic behavior of saturated clay under complex stress path considering the combined effects of both initial consolidation condition and seismic loading, bidirectional and horizontal cyclic tests are conducted for anisotropic consolidation condition under different initial orientation of principal stress. The apparatus for static and dynamic universal tri-axial and torsional shear soil testing is employed to perform cyclic coupled vertical and torsional shear test in initial orientation of 0?, 45?, and 90??induced by bidirectional shaking and cyclic torsional test. Uniform and reproducible cohesive specimens having a specimen shape of hollow cylinder were obtained using vacuum suction method. The effect of initial orientation of principle stress axes on dynamic strength behavior and pore water pressure evolution of bidirectional cyclic tests and torsional cyclic tests is systematically investigation through a number of soil tests. Based on the experimental results, it was shown that the dynamic strength of saturated clay with bidirectional was less than the torsional cyclic loading under identical initial orientation of principal stress. In order to reflect the variation of water pore pressure with different stress states, the method of acquiring pore water pressure which was getting stable after ceasing coupling cyclic loading was adopt.