The <i>ε</i>_v/<i>ε</i>_a–<i>p</i>′ method for the determination of instability of granular soils under constant shear drained stress path

Past studies suggested various methods to determine the onset of instability of soil under constant shear drained (CSD) stress path using triaxial equipment. These methods were based on the characteristic features observed on the CSD stress path, axial and volumetric strains. However, the characteristic features are not similar for every soil leading to inconsistencies in predicting the onset of instability under the CSD stress path. This paper presents a strain ratio (ε v /ε a ) – mean effective stress (p′) based method for determining the onset of instability of sand in the CSD stress path. The proposed method identifies the onset of instability at the drop of the ε v /ε a –p′ curve and features a distinctive value to mark the onset of instability. A series of CSD tests have been carried out on sand samples to verify the applicability of the proposed method. The proposed method captured the onset of instability similar to the other methods available in the literature.