Exploring the Impact of Oriented Notch Distribution on the Shear Behavior and Failure Patterns of Rocks: Insights From Experimental Direct Shear Testing and Numerical Modeling

This investigation focuses on experimental shear tests and their numerical simulations using particle flow code (PFC2D). The study examines how normal stresses on joints (notches) and the geometry of the joints, including factors such as length, inclination angle, and aperture, affect the mechanical behavior, failure mechanisms, and fracturing patterns in rock samples that contain both rock bridges and joints of various lengths under direct shear loading conditions. Specimens were designed with various notch lengths and angles, including both open and closed notches. They were tested under three different vertical stress levels, with the loading rate controlled at 0.05 mm/s during the tests. The crack propagation paths and coalescence at final failure of the specimen agree well in both lab‐scale investigations and numerical methods. Tension cracks dominated at low normal stress, while mixed‐mode failure occurred at higher normal loads. Results indicate that in samples with shorter joint lengths, the shear resistance of rock bridges (the space between two joints) has increased. Additionally, under constant normal loading conditions during the direct shear tests, the failure mode in the jointed geomaterial specimens transitioned from a planar breakage mode to a fish‐eye mode as the notch angles increased. This transition occurred due to stress shielding between the notches. With fixed notch angles in the jointed rock‐like samples, the fish‐eye failure mode then changed to a diagonal tensile failure mode as the normal stresses increased during the tests. This change was attributed to the suppression of rock bridges that occurred under high normal loads.