Behaviour of granular bodies in induced shear zones

This paper deals with the behaviour of granular bodies in induced shear zones. Shearing of an infinite narrow layer of sand between two very rough boundaries under conditions of free dilatancy is numerically modelled with a finite element method and a hypoplastic constitutive relation within a polar (Cosserat) continuum. The relation can reproduce the essential features of granular bodies during shear localisation. The material constants are easily determined from element test results and can be estimated from granulometric properties. The attention is laid on the influence of the initial void ratio, mean grain diameter, layer height, pressure level and grain roughness on the thickness of induced shear zones. In addition, the effect of dilatancy constraint on shear localisation is investigated. The results are also compared to solutions within a non-polar continuum. The FE-calculations demonstrate that polar effects manifested by the appearance of grain rotations and couple stresses are significant in shear zones and their thickness is mainly affected by the initial void ratio, the mean grain diameter and the layer height. Received: 16 November 1999