Abstract
Experimental evidence indicates that the shear localisation acts as a precursor to the failure in biaxial compression tests of granular materials. Once formed they are persistent and lead to progressive failure of most geotechnical structures. It is generally accepted that the primary mode of deformation within these shear bands is simple shear which is accompanied by rotation of principal axes. Hence, the conventional plasticity theories based on the assumption of coaxility is not sufficient to describe the behaviour within those shear bands. This paper highlights the influence of the non-coaxility on the initiation and orientation of shear bands in both drained and undrained sand. The con-coaxial plasticity theory is integrated into a critical state constitutive model enriched with the state parameter concept. The model is capable of taking account of the variation of lode angle under plane strain condition. Numerical plane strain biaxial compression tests are conducted to observe the effect of non-coaxility on shear localisation. Bifurcation criteria based on the acoustic tensor are checked to predict the onset and inclination of the shear band. Predictions from the non-coaxial model are compared with those of coaxial model. The influence of the initial void ratio for the formation of shear bands is explored. Results are compared qualitatively with experimental observations.
Highlights
The mathematical modelling of the strain localisation consists of two main phases: detection of the onset of material instability and capturing the post localisation
The objective of this study is to evaluate the role of the constitutive model to capture the onset of shear localisation in granular material
They report that the stress strain relationships are hardly changed, but the prediction of localisations is significantly improved from the non-coaxial theory. They further state that the non-coaxial flow rule does not alter the prediction of diffuse instability. Their non-coaxial predictions of shear localisations are consistent with experimental results of both dry and saturated undrained sand whereas coaxial models tend to underpredict the strain at the initiation of the shear band
Summary
The mathematical modelling of the strain localisation consists of two main phases: detection of the onset of material instability and capturing the post localisation. Both of which are important to get a clear view of the failure of geo-materials. The former identifies the emergence and inclination of the localised band, whereas the latter determines a physically meaningful representation of the material during a localised deformation. The influence of non-coaxial flow rule for the detection of localisation is explored. The influence of the initial state on the formation of shear band is explored for both drained and undrained conditions
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