Unstable behaviour of sand and its implication for slope instability

Abstract

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.

Experimental Study on the Cyclic Resistance of a Natural Loess from Northern France

“…was observed, as a result of Du increase. As deˆned by Lade and Pradel (1990), Vaid and Eliadorani (1998), Leong et al (2000) and Chu et al (2003), the point corresponding to the abrupt change in e 1 rate can be referred to as the instability state of the soil and it can be concluded that for Test 6, the instability was reached at about 2z axial strain after 3 cycles.…”

“…In order to explore the instability phenomenon of the soil taken from diŠerent depths or at diŠerent unsaturated conditions, higher cyclic deviator stresses were applied in order to drive the soil beyond the instability state. In this work, the instability onset is referred to as the occurrence of runaway deformation according to Lade and Pradel (1990), Vaid and Eliadorani (1998), Leong et al (2000) and Chu et al (2003). The instability is considered as liquefaction-reduced one when 5z double amplitude axial strain (peak-to-peak strain) or zero eŠective mean stress is reached, as suggested by Bray and Sancio (2006).…”

“…The two phenomena have been later on referred to as pre-failure instability. The instability is often deˆned as a condition that occurs when a soil element subjected to a small eŠective stress perturbation cannot sustain the current stress state imposed on it and a runaway deformation takes place (Lade and Pradel, 1990;Vaid and Eliadorani, 1998;Leong et al, 2000;Chu et al, 2003). In most cases, the instability phenomenon occurs when shearing the saturated sand under undrained conditions.…”

Infiltration-induced Slope Instability: a multi-scale approach

“…The framework proposed by [19] (after [20]) has been adopted to study the failure mechanisms of loose and dense sand samples. They concluded that the instability can occur under both undrained and drained conditions as long as the stress path leads the stress state into the zone of instability, distinguishing the occurrence of conditional stability (continuously decreasing mean effective stress in drained conditions) from that of run-away failure (under undrained conditions due to the progressive increase of pore-water pressure).…”

Natural Hazard Risk Management: a Multidisciplinary Approach to Define a Decision Support System for Shallow Rainfall-Induced Landslides

“…In literature [1][2][3][4][5][6][7][8][9][10], the flowslide generation in saturated granular deposits is generally linked to the susceptibility to liquefaction and, hence, under shear load, to the establishment of an unstable undrained response, characterized by progressive decrease of shear strength due to the development of positive excess pore pressure (static liquefaction).…”