Numerical analysis on shear slip mechanism of clay-infilled rock joints

The mechanical behaviour of clay-infilled rock joints plays a critical role in the stability of rock mass engineering, with the strength and deformation characteristics largely governed by the clay and water contents of the infill material. Building on previous experimental and theoretical studies, this paper presents a novel incremental stress-strain constitutive model that explicitly incorporates both clay content and water content, developed within the framework of elastoplasticity and plastic potential theory. To systematically investigate the progressive failure mechanisms under complex stress paths, triaxial shear tests on regular saw-tooth rock joints filled with clay were simulated numerically using the Continuous-Discontinuous Element Method (CDEM). The results reveal that variations in water content and clay content markedly influence the strain hardening/softening response, peak strength and residual strength of the infilled joints. The close correspondence between numerical predictions and experimental data validates the rationality and applicability of the proposed constitutive model. Furthermore, the developed shear strength criterion and constitutive model were implemented into a three-dimensional numerical framework to assess the stability of a tunnel with soft surrounding rock traversing a fault zone. This work provides a scientifically grounded approach and practical reference for forecasting and mitigating large-deformation hazards in analogous geotechnical engineering projects.