DEVELOPMENT OF YIELD LOCUS BY AGEING OF CEMENT-MIXED SOIL IN DRAINED TRIAXIAL COMPRESSION

To evaluate ageing effects on the yielding and strength characteristics of cement-mixed soil, a series of non-conventional drained triaxial compression tests were performed on compacted specimens of cement-mixed gravelly soil. The specimens were cured first under atmospheric pressure for different periods, and then subjected to drained triaxial compression along various stress paths at different confining pressures. The specimens were re-cured at different fixed anisotropic stress states for a period of two days and then monotonically loaded along different stress paths at the original strain rate towards ultimate failure. The followings were found: i) the elastic domain in the stress space expands during sustained loading not only by yielding associated with viscous deformation but also by ageing effects. ii) An additional gain may be obtained by positive coupling effects between these two factors. iii) This gain is however damaged by irreversible shear strains during subsequent loading. iv) The peak strength is also affected by these three factors. v) As a result of yielding and ageing, the size of elastic domain increases while the shape of yield locus changes when the stress state is approaching the peak stress line (PSL). To explain issue v), an interactive double-yielding concept comprising a bounding mechanism and a frictional mechanism is introduced.