Unstable behaviour of sand and its implication for slope instability

Results of some constant shear-drained (CSD) tests conducted on both loose and dense sand are presented. Using the critical state line and a modified state parameter, a new framework for analysing the instability of granular soil slopes is proposed. The test data were examined and interpreted using the new framework. Instability lines for sand with different void ratios were established within this framework. The conditions for the occurrence of instability in both contractive and dilative granular soil slopes under various shear stress levels were examined using the proposed framework.