Instability Behaviour of Kutch Soil under Plane Strain Conditions

The influence of effective confining pressure on Chang Dam soil obtained from the Kutch region in India is explored in a flexible boundary plane strain apparatus. The boundaries of the apparatus were relatively flexible along the two loading directions. The test set-up offers the advantage of measurement of strains and stresses along the principal loading and lateral direction. Consolidated undrained tests were performed for sand at four effective confining pressures. The applicability of instability criteria based on the second-order work is examined for Chang Dam soil. Furthermore, the instability onset indicated by the evolution of lateral strains is almost coincident with the second-order work criterion. However, the global stress-strain response does not depict unstable behaviour. The dilatancy angle decreases non-linearly with the stress ratio. The stress ratio at phase transformation is observed to be a function of the state with varying effective confining pressures.