A classification framework for heterogeneous debris structures in post-disaster coal mine roadways

In the aftermath of safety accidents in coal mines, the pervasive phenomenon of roadway collapse and obstruction poses an urgent on-site challenge: namely, the expeditious assessment of the internal structure of heterogeneous debris and the creation of rescue channels. At present, there is a paucity of methods to guide the rapid assessment of heterogeneous debris structures, resulting in a significant amount of time spent on-site evaluating these structures. This has the effect of delaying rescue timelines and hindering the rapid establishment of rescue passages. In order to address this issue, a case analysis approach was adopted in order to study the structural characteristics of post-disaster roadway heterogeneous debris and the factors that influence them. A three-dimensional framework was established, comprising disaster type, surrounding rock lithology, and support type. Each dimension was characterised by a set of indicators based on the inherent properties of the disaster. The disaster type dimension includes two categories: gradual failure and triggered failure. The surrounding rock lithology dimension includes three categories: hard rock, medium-hard rock, and soft rock. The support type dimension includes four categories: bolt/cable support systems, steel frame support, and composite support. The amalgamation of disparate indicators across these three dimensions engenders 18 distinct types of heterogeneous debris structures and their characteristics, thereby precipitating a rapid three-dimensional classification method for post-disaster roadway heterogeneous debris. The classification results are denoted by alphanumeric codes (111−233), where the first digit indicates the disaster type (1 = gradual failure, 2 = triggered failure), the second digit indicates the surrounding rock lithology (1 = hard rock, 2 = medium-hard rock, 3 = soft rock), and the third digit indicates the support type (1 = bolt/cable support system, 2 = steel frame support, 3 = composite support). A detailed analysis was conducted of a roof fall accident in the haulage roadway of the 113101 working face of a specific mine. The rapid three-dimensional classification method was used to categorise the heterogeneous debris left behind by the disaster, resulting in a classification of '131'. Key characteristics include uniform and dense accumulation due to the plastic flow of soft rock, bolts scattered within the rock mass and enveloped by it, and stretched metal mesh covering the bottom. Particle flow numerical simulation software was used to simulate the collapse characteristics of the accident. The simulation results indicated plastic failure of the soft rock, as well as deformation or fracture of the bolts and cables within the rock mass and stretched metal mesh covering the surface. These simulation results largely align with the characteristics of the “131” classification. The method was applied to two further cases, resulting in classifications of ‘121’ and ‘132’. The structural characteristics of the heterogeneous debris in both cases were consistent with the results of the on-site investigation, thereby validating the classification and demonstrating the feasibility of using this rapid, three-dimensional method to classify heterogeneous debris on post-disaster roadways. This method can provide scientific support for rapidly assessing the internal structure of heterogeneous debris and clearing rescue channels during emergency response operations in coal mine accidents.