Undrained cyclic and monotonic triaxial behaviour of saturated loose sand

The cyclic shear strength and deformation of a loose saturated sand whose shear behaviour is contractive were investigated in this study. A series of cyclic triaxial tests with various initial static and subsequent cyclic shear stresses was carried out on the saturated sand with a very low relative density. Additionally, monotonic triaxial compression and extension tests were also performed on the same sand with the similar initial conditions. Quite large residual strains were observed in cyclic triaxial tests on anisotropically consolidated specimens. Flow deformation appeared during cyclic loading and it often caused the specimen to rapidly deform to failure. The comparisons between the results of cyclic and monotonic triaxial tests indicate that the potential for the occurrence of flow deformation depends on the mutual situations between the initial consolidation and the phase transformation points in the p-q stress state diagram.