Transversely Isotropic Creep Model for Rocks

Abstract

The transverse isotropic (TI) creep behavior of rocks was investigated using laboratory tests and constitutive modelling. Triaxial stepwise and multiple-stage creep tests were performed to investigate the TI creep behavior of carbonaceous slate. It was found that at an identical stress state in triaxial creep tests, the axial strain rates of the carbonaceous slate with bedding plane perpendicular to axial loading is higher than those of the specimens with bedding plane parallel to axial loading. It was also found that an inelastic strain-dependent strain rate would prevail over the time-dependent strain rate for describing the creep behavior of rocks in complex loading-unloading conditions. A viscoplastic model for modelling the TI creep behavior of rocks was proposed. In the model, the creep potential was formulated as functions of the generalized octahedral shear stress and the first invariant of stress tensor. A nonassociated flow rule and a strain-dependent and stress-dependent strain rate were adopted in the model. A methodology for the model parameter determination was developed. The proposed model and the parameter determination methodology were validated against test data from carbonaceous slate. The results showed that the model proposed in this study can well describe the TI creep behavior of rocks and that the methodology of parameter determination is simple and effective.