Experimental Study of Temperature Distribution and Evolution Law of Fractured Rock Mass During Heat Transfer Process

To investigate the hindering effect of fracture on heat transfer within rock mass, real-time temperature monitoring was conducted on fractured granite heated by different constant-temperature heat sources. The heat transfer characteristics were analyzed based on the temperature field distribution, temperature variation pattern, heating rate, temperature difference, and temperature gradient evolution within the fractured granite. Additionally, the difference in temperature field distributions of both intact and fractured granite under different heat source temperatures were discussed. The study reveals that fracture exerts significant control over temperature field distribution in granite, with heat transfer governed by the combined effects of rock heterogeneity and fracture presence. During heating, fractured granite exhibits three distinct temperature response stages: rapid heating, slow heating, and temperature stabilization. Steady temperatures decrease nonlinearly and linearly with increasing distance from the heat source on the left and right side of the fracture. All monitoring points display unimodal heating rate trends (rise–peak–decline–stabilization), with peak rates of 20~120 °C/h above the horizontal monitoring line F-F versus 10~20 °C/h below it. The hindering effect of fracture on heat transfer shows spatial heterogeneity; under the condition of the 80 °C heat source, the temperature difference in the central region is the largest (ΔTmax = 10.5 °C), and the top is the smallest (ΔTmin = 4.5 °C). Concentrated isothermal gradient contours form around fractures, with the time-to-peak gradient correlating positively with heat source distance. Maximum and minimum temperature gradients within the fracture reached 825 °C/m and 345 °C/m, respectively, at 90 °C source temperature. The research results can provide a theoretical basis and technical support for HDR geothermal development.