A Novel Hydromechanical Coupling Constitutive Model for Jointed Rock Masses Informed by Compression–Shear–Seepage Tests

Jointed rock masses are among the most commonly encountered types of engineering rock masses and are widely found in water-rich environments. Their hydromechanical coupling behavior is extremely intricate due to varying joint roughness and stress conditions, making accurate prediction challenging. To address this issue, in this study, a series of compression–shear–seepage coupling tests were conducted on jointed rock masses, covering different joint roughness coefficients (JRCs), confining pressures, and water pressures. The experimental results reveal that the jointed rock mass undergoes three sequential stages during the complete shear-slip process, elastic compaction, shear dilation, and shear wear. By incorporating the concept of mobilization of the JRC and friction angle, a novel hydromechanical coupling constitutive model was developed to evaluate shear strength, shear dilation deformation, and equivalent hydraulic aperture throughout these stages. The developed constitutive model establishes a physical linkage between seepage behavior and mechanical responses, capturing hydromechanical coupling effectively. The hydromechanical coupling analysis reveals that the permeability of rock joint evolves parabolically with shear deformation, increasing up to tenfold in highly rough joints due to shear dilation, while confining pressure enhances shear strength and stiffness but reduces permeability. The proposed hydromechanical constitutive model provides a fundamental tool for predicting coupled behavior in jointed rock masses, offering both theoretical insight and practical utility for engineering applications such as tunnel excavation and slope stability.