Method for Evaluating the Equivalent Thermal Conductivity of a Freezing Rock Mass Containing Systematic Fractures

Rock deterioration is caused by freeze–thaw cycles, and this deterioration or loss of strength induces failure when the rock thaws. To accurately analyze freeze–thaw cycles, a proper method for evaluating the thermal conductivity of a fractured rock mass is needed. In this study, a simplified model of a fracture was derived from knowledge of actual fractures in rock masses, and the possible thermal resistance types of a fracture were analyzed. Then, according to the definition of thermal resistance, models were established for the normal and tangential thermal resistances of a fracture by considering the ice-water phase transition. Based on the thermal resistance models, a method for evaluating the equivalent thermal conductivity of a rock mass with a set of systematic fractures was established. The effect of the convective heat transfer of the water in the fractures was considered based on energy contributions. According to the superposition principle and the introduction of fracture parameters (strike angle, dip direction angle, and dip angle), the proposed method was extended to rock masses with multiple sets of fractures, and a sensitivity analysis was conducted. The thermal conductivity of a rock mass with connected fractures was more sensitive to the fracture parameters than that of a rock mass with intermittent fractures. Finally, the proposed method was verified by comparison with an experiment using a block of cement with artificial fissures under freezing conditions; the calculated temperature agreed well with the experimental results.