Deformation of granular materials due to rotation of principal axes

The behaviour of granular materials when subjected to rotation of their principal axes of stress or strain is not fully understood. In the late 1980s a new apparatus was developed to allow general plane strain conditions to be applied to an analogue soil (Schneebeli cylinders). This paper presents a short description of this apparatus and its capabilities. Experimental results from different types of cyclic tests involving the continuous rotation of principal axes are given, mainly in terms of volume change and the co-axiality of stress and strain increment tensors, The results show that cyclic rotation induces a general tendency to compaction, and that the principal axes of stress and strain increment are not coincident as it is generally assumed in isotropic elastoplastic modelling.