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.Key words: deformation, laboratory tests, liquefaction, sands, shear strength, slope stability.

No abstract

No abstract

Strain softening in the form of decreasing shear resistance and instability, the inability to sustain given loads, can occur before the failure state is attained. This so-called pre-failure strain softening or pre-failure instability has been observed to occur for very loose sand in undrained tests and for dense sand in strain path controlled tests. Experimental data are presented in this paper to compare the pre-failure strain softening and pre-failure instability behaviour. It is established that the factors that control the occurrence of pre-failure strain softening and pre-failure instability are essentially the same, although the two types of behaviour are different. The similarities and differences between strain softening and instability are discussed for both loose and dense sand.