Thermal Contact Resistance of Granite Joints Under Normal Stress

Heat transfer in jointed rock masses exhibits characteristics of discontinuous, heterogeneous, and anisotropic due to the effects of rock discontinuities. In this work, thermal contact resistance (TCR) evolution of granite joints under normal stress was investigated. A novel method was proposed for the measurement of TCR for rough rock joints. A numerical calculation program was established for the determination of contact area based on the initial morphology of the joint surfaces and the monitored joint closure during the experiment. An estimation model of TCR for granite joints based on the equivalent joint aperture was established. It is found that TCR of granite joints shows decreasing trend with normal stress. The decreasing rate is relatively large at the initial loading stage and gradually reduces with normal stress. The values of TCR eventually stabilize. TCR of granite joint has no obvious correlation with joint roughness coefficient. It is more significantly affected by the contact area. Plastic deformation and rupture of the micro-convex body on the joint surfaces occurred due to the application of normal stress, which improve the heat transfer efficiency and lead to the decrease in TCR. In general, predication results of the TCR estimation model show good consistency with the experimental data. The model is more suitable for the cases with small joint apertures. This study can provide knowledge to the better understanding of heat transfer in rock masses containing different kinds of discontinuities.