Analysis of shear fracture characteristics and energy evolution of salt rock under real-time coupled thermo-mechanical conditions

Abstract

Studying the shear fracture behavior of salt rock is of great importance for the identification of precursor information for geological disasters such as underground salt cavern caprock slippage, fault instability displacement, and zonal destruction of the surrounding rock. Despite its undeniable importance, research on the shear fracture characteristics of salt rock under real-time high-temperature and high-pressure triaxial conditions remains scarce. To address this research gap, this study employed a self-developed rock real-time high-temperature and high-pressure multi-field coupled triaxial universal testing machine to perform triaxial shear fracture tests on salt rock punch through shear (PTS) specimens across a wide range of confining pressures (0 to 25 MPa) and real-time temperatures (20 °C to 600 °C). Additionally, the internal pore fracture structures of the salt rock after different coupled thermo-mechanical (TM) treatments were examined using micro-computed tomography (MCT) and metallographic microscopy. The results reveal the complexity of fracture behavior in salt rock. At normal temperature and pressure, salt rock specimens primarily fractured into short rods and hollow cylindrical forms, with wing cracks appearing on the surfaces of the cylinders. Under high-temperature and high-pressure conditions, the salt rock exhibited more intense shear slippage phenomena, although the specimens did not undergo complete fracturing. Notably, the internal pore fractures in the salt rock under real-time coupled high-temperature and high-pressure displayed a competitive interaction between self-healing and thermal damage, leading to a significant nonlinear increase in mode II fracture toughness with temperature. Through the analysis of energy absorption and dissipation, this study further elucidates the shear fracture mechanism of salt rock under coupled TM conditions. Overall, the findings of this paper not only deepen our understanding of the mechanical behavior of salt rock under high-temperature and high-pressure conditions but also provide crucial theoretical support for the design and risk management of underground salt cavern projects.