An improved rock damage model from a cyclic temperature – triaxial loading experiment for compressed air energy storage caverns

While studies on rock damage have mostly examined cyclic mechanical loading, or addressed thermal and mechanical loadings separately, compressed air energy storage (CAES) projects require the coupling of both effects. Granite was used to demonstrate a systematic experimental procedure in which cyclic temperature effects was incorporated into fatigue damage study of rocks subject to cyclic mechanical loading. Granite specimens were pre-treated with cyclic temperatures up to 200°C, 400°C, and 600°C, with the P-wave velocity tested after each cycle. Subsequently, the treated specimens went through triaxial cyclic loading. The upper limit of the triaxial cyclic loading was 200 MPa, and the confining pressures were 5 MPa, 10 MPa, and 15 MPa. Granite exhibited hardened and weakened behaviour. The specimens were weakened if the deviatoric stress exceeded the fatigue threshold, which was determined by the cyclic temperature and the confining pressure in this study. A damage model was derived to quantify the degree of hardening and weakening. The model improved the existing damage models by incorporating the cyclic temperature effect. This study lays a foundation for safe operation of CAES projects.