A Semiempirical Approach to Modeling Shear Strength in Unsaturated Infilled Rock Fractures

This study introduces a semiempirical model characterizing the shear behavior of infilled rock fractures, accounting for both the roughness of rock fracture walls and the presence of unsaturated fine-grained infill materials. The model expands on existing frameworks for saturated infills by integrating soil–water retention curve parameters and incorporating hardening effects due to changes in infill volume or saturation degree. To better represent natural fracture conditions, a modified formulation is also proposed that incorporates fracture surface morphology parameters, including the joint roughness coefficient and joint wall compressive strength. The model's predictions are compared with data from an independent experimental program measuring the shear strength of infilled fractured rocks during drying and wetting. Further validation is achieved by comparing estimated and measured shear strength values from published literature. Results indicate that the proposed model offers more consistent predictions of shear strength across varying hydraulic conditions and confining stresses, showcasing its improved capability in capturing the complex behavior of unsaturated infilled rock fractures during shear.