The soil static and dynamic universal triaxial and torsional shear apparatus is employed to perform undrained cyclic torsional shear experimental tests of saturated loose sand with a relative density of 30% under three-directional anisotropic initial consolidation conditions involving a wide range of initial orientation of principal stress and coefficient of intermediate principal stress. The effects of initial consolidation conditions on the development pattern of cyclic pore water pressure of undrained saturated loose sand and the complex volumetric change behaviour involving dilatancy, contraction and volume-contraction during unloading are examined on the basis of comparative experimental tests. It is shown that the ratio of residual pore water pressure to the residual pore pressure at failure state can be expressed as an empirical hyperbolic function with respect to either the generalized shear strain or the ratio of the cyclic number to the cyclic number required at the failure state. The parameters in the hyperbolic functions determined by experimental tests results are closely dependent on initial orientation of principal stress and are likely to be independent on coefficient of intermediate principal stress. It is also shown that the volume-contraction during unloading is a phenomenon displayed commonly in undrained loose sands subjected to cyclic shearing under three-directional anisotropic consolidation condition. Furthermore the types of volumetric change behaviour are closely associated with the initial orientation of principal stress.
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