The Seepage Characteristics of Single Rough Joint of Granite Based on NMR Technology: A Modified Cubic Law

Understanding the seepage mechanisms of rough granite joints under stress–seepage coupling is essential for predicting fluid flow in jointed rock masses. In this study, seepage–stress coupling tests are conducted on granite specimens containing a single rough joint, and the fluid migration process is continuously monitored using low‐field nuclear magnetic resonance (NMR). The evolution of the transverse relaxation time ( T 2 ) spectra is used to characterize the dynamic change of joint aperture and pore connectivity. Results reveal that fluid migration follows a sequential path: preferentially entering large pores, then invading smaller pores under increasing seepage pressure, and finally refilling large pores after saturation. These transitions reflect the cyclic redistribution of water governed by asperity deformation and stress‐induced joint closure or dilation. Quantitative analysis shows that permeability increases with higher seepage pressure and joint roughness coefficient ( JRC ) but decreases nonlinearly with confining pressure. Based on these observations, a modified cubic law is established by incorporating JRC and stress‐dependent joint width correction, which accurately captures the nonlinear coupling between roughness, stress, and flow. This study provides new insights into the hydro‐mechanical mechanisms controlling seepage evolution in rough granite joints.