Development of approaches to monitoring the tension and shear fractures in rock supports to assess the risk of their failure

The article describes the mechanism of occurrence and gradual development of the tension fractures in the surface layer and the shear fractures in the core of the rock supports (pillars) under uniaxial compression. This model differs from the existing ones because it identifies two stages of the failure process: during the first stage, tensile stresses initiate fracture formation, and during the second stage, shear stresses cause shear fractures. This approach does not rely on preliminary assumptions about the presence or absence of fractures before the deformation begins, which expands the scope of its application. Our previous studies have shown that the tensile stresses in the core of the pillar negatively correlate with the thickness of the surface layer containing newly formed radial cracks. When the tensile stresses do not exceed the tensile strength, the thickness of this layer does not increase, which determines the transition to the second stage of failure. During the second stage, tangential stresses continue to increase, which causes the shear failure of the pillar core. Case study shows that after the first stage of failure, the pillar retains its load-bearing capacity only partially, since the damage significantly reduces the area of its cross-section, for example, to 42% of the original value in the example considered. The results of the modeling are consistent with the known studies and conclusions that when designing rock supports it is extremely important to consider the gradual failure and reduction in the bearing capacity during their operation to ensure the safety of mining operations. The risk indicators of the rock pillar failure are vertical tension fractures, spalling and transformation into the hourglass shape. The shear fractures that develop during the second stage and are oriented at angles close to the internal friction angle are more hazardous. The simulation results are consistent with the known data. However, variability of the physical and mechanical properties of rocks and the external influences to which they are exposed indicates the need for further research on this topic.