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 elastoplastic 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 postmortem 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. (C) 2016 Elsevier Ltd. All rights reserved.