A model for the deformation and flow of granular materials undergoing monotonic shear loading

A simple mechanical analogue is presented which provides an insight into the diverse mechanical behaviour of granular materials. It involves a ball that deforms and rolls between two parallel platens and models shear deformation, compaction and dilation. The analogue can be used as an aid to the understanding of deformation and flow in both drained and undrained tests. A mathematical version of this model is formulated, using plasticity and the mathematical theory of envelopes, which identifies the circumstances for both associated and non-associated flow. The parameters that control the size and shape of the yield surface change during deformation. This allows the model to produce qualitative predictions which compare well with the published behaviour of real materials. In particular, some light has been shed on the poorly understood deformation behaviour of sands under undrained conditions. -Author