Development of Similarity Materials for Jointed Rock Masses in Underground Cavern Model Tests

Utilizing appropriate similar materials in physical model testing is critical to ensuring an accurate simulation of the prototype mechanical behavior. For example, the physical modeling of jointed and fractured rock masses requires replicating their nonlinear mechanical characteristics. Therefore, this study develops mix proportions for a rock-like material similar to that encountered in the Xiangjiaba Hydropower Project. Based on similarity ratio analysis and mechanical testing, a jointed and fractured rock mass material was developed using a modified thin-sheet stripping method, and its nonlinear behavior was validated through mechanical experiments, numerical simulations, and distortion energy theory. The testing results of the developed similar material are as follows: (1) In specimens with single-jointed and fractured rock mass, the peak uniaxial compressive strength varies according to the joint orientation in the following order: 90° > 60° > 45° > 0° > 30°. In specimens with intersecting joints, the overall strength is primarily controlled by the orientation of the main joint, while the secondary joint plays a lesser role in further reducing the strength. (2) The analysis of distortion energy for both single-jointed and cross-jointed and fractured rock masses indicates that the crack initiation angle generally decreases with increasing joint inclination. Furthermore, at the onset of failure, the crack initiation angle in the lower part of the specimen is consistently larger than that in the upper part. The experimentally observed crack angles are in good agreement with the theoretical predictions. (3) A numerical model of the jointed and fractured rock mass was developed using the PFC2D version 5.0 discrete element software. Comparing the results of the numerical simulations and mechanical tests revealed consistent failure patterns: both exhibit the typical shear-tensile composite failure modes characteristic of jointed and fractured rock masses. These findings confirm that the developed jointed and fractured rock mass similar materials realistically capture the nonlinear mechanical behavior of fractured surrounding rock, providing a reliable material basis for the physical model testing of underground caverns.