DEM micromechanical modeling and laboratory experiment on creep behavior of salt rock

Subjected to long-term mechanical and thermal loads, salt rocks where many Underground Gas Storages (UGS) are solution mining usually demonstrate strong time-dependent creep behaviors. To ensure construction and operation of UGS to meet the design standards, it is of critical importance to obtain an accurate understanding of the creep behaviors of host salt rock. In this study, the micro-mechanisms of how temperature influences salt creep behavior is investigated in a discrete element method (DEM) based micromechanics system. The salt rock sample is simulated by bonded particle model implemented in Particle Flow Code (PFC). A new hybrid model is proposed to describe the thermal-mechanical creep behavior. The major components employ Burger's type contacts between particles for modeling creep behavior and active thermal pipes for capturing effects of heat transfer between particles connected by linear parallel bonds representing the salt rock around caverns. The rock specimen demonstrates very strong ductile behavior. Comparison with laboratory experimental data shows that the numerical model is capable of capturing the development of micro-fractures during creep test. The results indicate that both confining pressure and temperature make significant contributions to creep straining. Particularly, the induced thermal cracks indicate increasing creep strain rate with the elevated temperature. This study provides an alternative and promising numerical method to investigate the fundamentals of creep mechanism of salt rock for UGS applications.