Mechanism of zonal disintegration phenomenon (ZDP) and model test validation

The zonal disintegration phenomenon (ZDP) is investigated by proposing a criterion based on fracture mechanics. Accordingly, the mechanism is revealed to be the circulation of the fracture of the elasto-plastic boundary caused by the peak SIF (Stress Intensity Factor) and the constant formation of a “new” plastic boundary. Consequently, the reason ZDP occurs in deep caverns is also interpreted based on this theory. In addition, a formula is proposed to predict and determine the post-mortem features of ZDP, including the numbers (N) and sizes (r) of the fractured zones. The subsequent sensitivity analysis shows that the impact factors are the geo-stress and parameters of the rock mass. The variation laws of the post-mortem feature versus these impact factors are also determined. A 3-D geo-mechanical model test is conducted based on an analogous material. A deep tunnel in the PANJI coal mine, where zonal disintegration is observed, serves as the prototype engineering project. This model presents the forming process of ZDP. The criterion and post-mortem features proposed by the formula are validated through the model test. Furthermore, the results confirm that the wavy deformation law can be used to predict the ZDP.