Development of progressive failure in sensitive clay slopes

Abstract

The development of progressive failure in sensitive clay slopes is analysed using principles from fracture mechanics, where failure stress depends on a material property (toughness) and length of an existing weakness, unlike traditional soil mechanics where failure stress is generally assumed to be only a function of material strength. An existing weakness, or partially developed failure surface, can propagate due to sudden loads, as might be induced by seasonal erosion cycles, small local landslides at a river bank or earthquake shaking. The paper examines the growth of the failure surface over time due to such loads. The analysis shows that a large landslide in sensitive clay can occur after a number of seasonal erosion cycles with no obvious trigger. It also shows that a larger load due to either a small landslide or earthquake can cause a developing failure surface to propagate freely toward general collapse. Large landslides in sensitive clay are often preceded by a smaller landslide at the river bank, but can be triggered by large earthquakes or may occur for no obvious reason. The agreement between predictions and real behaviour suggests that the model for progressive failure of large landslides in sensitive clay deserves further consideration.

Large deformation finite-element modelling of progressive failure leading to spread in sensitive clay slopes

“…It is assumed that the base layer is very thick; however, in the FE analyses only 3 m of this layer is modelled, as it does not have a significant effect on the results, which has been verified by an analysis with a 10 m thick base layer. The geometry considered here is an idealised section of river banks in eastern Canada where spread failures have occurred (Locat et al, 2011;Quinn et al, 2012). Note that any change in geometry and soil properties, including the property of the base layer, might alter the failure pattern.…”

“…They hypothesised that the failure of the slope will occur when the length of the shear band becomes sufficiently large such that the downward unbalanced force causes active shear failure. The authors also used the same concept to analyse the stability of the slope with additional stresses due to earthquake loading (Quinn et al, 2012). They also conducted elastic FE analysis to validate some of their assumptions.…”

Modeling of large-deformation behaviour of marine sensitive clays and its application to submarine slope stability analysis

“…Using the concepts of linear elastic fracture mechanics (LEFM) (Palmer and Rice 1973), Quinn et al (2011) proposed an analytical model for development of a shear band in an infinite slope with a vertical step cut. Quinn et al (2012) conducted finite element (FE) analysis to demonstrate the effects of toe erosion on propagation of a shear band through a weak predefined shear zone. Locat et al (2011) demonstrated the mechanisms of shear band formation for an idealized condition in an infinite slope by applying an external force parallel to the ground surface near the toe above a predefined shear zone.…”

Catastrophic failure in planar landslides with a fully softened weak zone

“…A particular form of shear band propagation, which has received considerable attention recently (Quinn et al, 2011(Quinn et al, , 2012Locat et al, 2011Locat et al, , 2013, is a progressive spreading failure accompanied by an uphill growth of the shear band driven by the removal of the downslope support. In contrast, catastrophic failure can occur by spontaneous growth of an initial shear band at both ends under existing forces (Puzrin et al, 2004;Puzrin & Germanovich, 2005;Andresen & Jostad, 2007;Viesca et al, 2008;Garagash & Germanovich, 2012;Viesca & Rice, 2012;Viesca, personal communication, 2014;Puzrin et al, 2015).…”