Cyclic Shear Responses of Saw-Tooth Artificial Rock Joints Under Constant Normal Load Conditions: Laboratory Investigation and Numerical Simulation

Understanding the movement behavior of upper blocks along rock joints or weak planes is crucial for the geological hazard forecast and prediction. This paper presents experimental and numerical investigations of a saw-tooth joint under shear and normal load conditions. Multi-stage direct shear tests under different normal load conditions were conducted using a direct shear box apparatus. The reverse dilation behavior of the upper specimen was observed by measuring the normal displacement at the four corners of the upper block. Laboratory test results show that, under lower normal loads, the normal displacement of the upper specimen on the applied shear force side initially decreases (settlement), while the settlement reverses to heave (dilation) when the shear displacement reaches a certain value. However, the settlement reverse behavior does not occur under large normal loads. Corresponding numerical simulation confirms that this settlement reversal is controlled by the specimen fracturing. The saw-tooth asperities are sheared off under a large normal load, while the upper specimen climbs along the slope of the bottom specimen under lower normal loads. Consequently, the changes in contact area, interface normal stress, interface shear stress, and normal displacement of the joint differ significantly between large and low normal load conditions. This research deepens our understanding of the shear-induced dilation and fracture behavior of saw-tooth joints, and the results can provide guidelines for evaluating the stability of geological rock mass.