Progress and prospects of thermo-hydro-mechanical characteristics of low temperature rock mass with phase transition

The fractures make the thermal-hydro-mechanical(THM) characteristics of rock mass and soil mass obviously different，and the existing frozen soil theory is difficult to solve the freeze-thaw disaster problem of low temperature rock mass. The migration mechanism of fracture water，the heat transfer mechanism of fracture，the dynamic evolution of fracture characteristics and the multi-field coupling of thermal-hydro-mechanical in heterogeneous rock mass are the key to study the freeze-thaw disaster of low-temperature rock mass. In this paper，the research progress of low-temperature rock mass with phase change is analyzed from four aspects： water migration mechanism，heat and mass transport characteristics，physical and mechanical characteristics and THM coupling characteristics. The research results on low-temperature rock mass at home and abroad are abundant，but the heterogeneity caused by fractures and the special characteristics of the THM properties of fractures under the condition of phase change are not fully considered. The mechanism of hydrothermal migration in fracture of low-temperature rock mass has not been proved，and there is lack of large-scale test equipment for studying the THM characteristics of low-temperature fractured rock mass. Although the fracture propagation caused by frost heave has been studied，the dynamic fracture evolution equation considering the whole process of freeze-thaw and the freeze-thaw cycle has not been established. The freeze-thaw disaster of low-temperature rock mass involves hydrothermal migration at the micro-level，fracture evolution at the meso-level and deformation and failure at the macro-level. So far，no THM coupling model has been established which integrates the results of micro-meso- macro. In order to explore the THM characteristics of low-temperature rock mass，the ice-water phase should be taken as the breakthrough point，the discontinuous characteristics caused by fractures should be closely linked，large-scale laboratory equipment should be developed，the mechanism of hydrothermal migration in fractures should be verified，the fracture evolution equation should be derived，the THM coupling model should be constructed，and numerical simulation programs should be developed，to finally realize the simulation of freeze-thaw disasters in low-temperature rock mass.