Limit equilibrium approach to study the evolution of shear band systems in soils

The paper is concerned with the analysis of shear band systems appearing in dry soil behind flexible retaining walls under plane strain conditions. The experimental problem studied is that of an initially vertical, plane retaining wall, deforming because of the gradual excavation of sand from one side of the wall. The aim of the paper is to clarify some of the possible physical reasons for multiple shear bands developing behind such walls. The problem of shear band arrangement in a regular pattern, and their possible sequence, are also considered. The behaviour of soil adjacent to the wall is modelled by a set of rigid blocks, cut off from the soil body by lines parallel to the classical Coulomb wedge ‘slip line’ and sliding subsequently on each other. The distance between subsequent shear bands is calculated from the equilibrium of an actual soil wedge, which may contain previously activated wedges. An elastic behaviour of the wall is taken into account in a simplified way when equilibrium is verified. The plastic softening of soil is expressed in terms of the angle of internal friction or cohesion decreasing linearly with soil wedge displacement. The present simplified analysis is aimed as an explanation of shear band patterns, and constitutes a first step towards more refined treatments.