A fracture aperture dependent thermal-cohesive coupled model for modelling thermal conduction in fractured rock mass

Due to thermal resistance characteristics of fractures, to realistically assess thermal effects of fractured rock mass, it should correctly reflect the thermal interaction between fracture interfaces. In this study, the coupled FEM-DEM method is extended to model transient thermal conduction in fractured rock mass. Rock matrix and fractures are discretized into solid elements and cohesive elements, respectively. To simulate thermal conduction across fractures, the cohesive element is coupled with a thermal model (thermal-cohesive model) by incorporating an aperture dependent interfacial thermal conductivity. Validation simulations indicate that the proposed model is capable of capturing the temperature jumps across the fractures with different apertures. Then, the influences of fracture characteristics on thermal conduction were numerically investigated. Finally, thermal conduction in highly fractured rock mass was studied by a model with multiple randomly distributed fractures generated through Monte-Carlo algorithm. The results indicate that the temperature gradient and heat flux field of rock mass containing a single fracture are quite sensitive to fracture orientation and aperture. Compared with the linear behavior between the ETC and fracture aperture in rock mass containing a single fracture, the relationship between the ETC and fracture aperture in highly fractured rock mass presents strong nonlinear characteristic.