Abstract:

The apparatus for static and dynamic universal triaxial and torsional shear soil testing was employed to perform stress-controlled coupled vertical and torsional coupling shear tests and monotonic torsional tests under undrained condition. Through a series of tests on saturated clay, monotonic torsional and rotation of principal stress under coupling cyclic shear behavior was examined. The strength of normal consolidated saturated clay in the monotonic torsional tests could be used to evaluate the overconsolidated monotonic torsional strength. The results of coupling tests show that the dynamic stress ratio and critical cyclic stress ratio linearly increased at uniform failure number with the overconsolidation ratio increased. This paper indicates that the effect of development mode of pore water pressure of coupling cyclic shear tests under different overconsolidation ratios is notable. The method of acquiring pore water pressure after ceasing coupling cyclic loading is able to better reflect the variation of water pore pressure with different overconsolidation ratios. It has been observed that a general strain fail criterion for clay is recommended for considering the integrative effects of torsional shear strain and normal deviatoric strain as well as cyclic strain and accumulative strain. Moreover, the general strain fail criterion is fit for the failure criterion of coupling cyclic test.

Key words: overconsolidation clay, hollow sample, rotation of principal stress, coupling cyclic shear, failure criterion, pore water pressure