Structured subloading yield surface model for soft rock considering confining pressure

Generally soft rock behavior is characterized by elasto-plastic deformation with heavily inherent cementation, which can be regarded as structured overconsolidated soils. The residual shear strength of the soft rock will be influenced by confining pressure which is significant during the practice. The concept of the difference of void ratio is extended in order to contain the overconsolidation ratio and the structural parameter. A reasonable development equation for the structural void difference is given. By introducing the concept of structured subloading yield surface, the structured subloading Cam-clay model for soft rock is proposed. In the proposed model the confining pressure will influence the structural damage ratio, and the residual structural parameter will be different under various confining pressures. By comparing the drained triaxial test results of the soft rock with the theoretical calculations, it is shown that the model can describe accurately the stress-strain relationships and the deformation features of the soft rock. Moreover, the phenomenon that the residual strength of the soft rock changes with confining pressure can be explained reasonablly by the proposed model.