FE-studies on the influence of initial void ratio, pressure level and meangrain diameter on shear localization

The paper is concerned with shear localization in the form of a spontaneous shear zone inside a granular material during a plane strain compression te st. The influence of an initial void ratio, pressure and a mean grain diame ter on the thickness of a shear zone is investigated. A plane strain compre ssion test with dry sand is numerically modelled with a finite element meth od taking into account a polar hypoplastic constitutive relation which was laid down within a polar (Cosserat) continuum. The relation was obtained th rough an extension of a non-polar hypoplastic constitutive law according to Gudehus and Bauer by polar quantities: rotations, curvatures, couple stres ses and a characteristic length. It can reproduce the essential features of granular bodies during shear localization. The material constants can be e asily calibrated. The FE-calculations demonstrate an increase in the thickn ess of the shear zone with increasing initial void ratio, pressure level an d mean grain diameter. Polar effects manifested by the appearance of grain rotations and couple stresses are only significant in the shear zone. A com parison between numerical calculations and experimental results shows a sat isfying agreement. Copyright (C) 1999 John Wiley & Sons, Ltd.