Thermo-elasto-viscoplastic model for soft rock

In the construction of many geotechnical projects, such as nuclear waste disposal and geothermal extraction and storage, it is necessary to consider the long-term mechanical properties of soft rock. Furthermore, the evaluated temperature will cause a complicated influence on the creep damage behaviors of soft rock. In consequence, it is theoretically and practically meaningful to establish a constitutive model which can describe the creep damage behaviors. Within the framework of continuum mechanics, a thermo-visco-elastoplastic model is proposed based on the sub-loading Cam-clay model and the concept of equivalent stress. Triaxial creep tests on Tage stone under different confining pressures are conducted by using the self-developed apparatus. Compared with the numerical results, the experimental results exhibit that for a certain stress state, an optimum temperature exists, which will slow down the creep damage rate the most. In addition, both retarding and accelerating effects on creep rupture due to limited warming are observed for the same material, and this phenomenon can be predicted by the proposed model. Finally, model characteristics are analyzed, and the influence of material parameters on creep laws is discussed.