Measured and Equivalent Shear Strength Parameters for Intermittently Jointed Rock Masses: Insights From Physical and Numerical Tests

ABSTRACT The shear behavior of intermittently jointed rock masses is crucial in engineering geology, yet the widely used Jennings criterion still lacks a systematic evaluation regarding its accuracy when applied to rock with various joint geometries. This study combines physical experiments and Particle Flow Code (PFC) simulations to investigate how joint geometries influence shear strength and to further assess whether the Jennings criterion can effectively capture these influences. Both approaches reveal similar trends: peak shear stress and cohesion decrease with higher joint connectivity and number, but increase with steeper dip angles. In the present experimental conditions, no clear trend was observed between the friction angle and variations in discontinuity geometrical features, which is likely related to the relatively limited range of geometrical configurations considered in the tests. A further comparison between measured and Jennings‐derived equivalent cohesion shows a widespread discrepancy: on average, equivalent cohesion exceeds measured values by 31.4% in physical tests and 10% in numerical simulations. This overestimation, due to stress concentration and altered failure paths introduced by different joint geometries, is most significant in low‐connectivity, high‐joint‐number, and gentle‐dip‐angle scenarios. These findings suggest that the Jennings criterion's applicability is limited, as significantly overestimated equivalent parameters could lead to overly optimistic stability assessments under certain conditions. Additionally, the impact of joint geometrical features on shear strength is both systematic and potentially quantifiable, offering a valuable reference for incorporating such features into equivalent parameter estimation methods to improve the accuracy of strength assessments.