No abstract

The porosity distribution law of overlying strata in the goaf has an important guiding role in distinguishing hidden disaster-causing factors in the goaf, such as the gas enrichment area and spontaneous combustion area. Existing research is concentrated on the overlying strata in the goaf of a single working face (GSWF), and the porosity distribution law of overlying strata in the goaf of an adjacent working face (GAWF) must be different from that in the GSWF. By selecting Longshan Coal Mine as an engineering background and applying theoretical analysis, numerical simulation and formula-fitting methods, the porosity distribution law of overlying strata in the GAWF was obtained for different section coal pillar types. The results demonstrate that (1) according to the supporting effect of different sections of coal pillar widths on overlying strata, the GAWF can be divided into three types: goaf of an adjacent working face with small-section coal pillar width type (GFST), goaf of an adjacent working face with moderate-section coal pillar width type (GFMT), and goaf of an adjacent working face with large-section coal pillar width type (GFLT). (2) In the goaf of a working face, the offset distance from the maximum porosity value area of each overlying rock stratum to the middle of the rock stratum is positively correlated with the distance between the overlying strata and the coal seam floor. In the area affected by the section coal pillar (ASCP), the porosity of each overlying rock stratum increases with an increase in the section coal pillar width, but is still smaller than its own initial porosity, and its increase rate continuously decreases. (3) From the coal seam floor upward, the porosity spatial form distribution of overlying strata in the GFST and GFMT is described as follows: partial “dustpan” shape–unilateral “concave-convex peak” combined shape. The porosity spatial form distribution of overlying strata in the GFLT is described as follows: “dustpan” shape–“concave-convex peak” combined shape-“Λ” shape.

Hidden disaster-causing factors (HDCFs) in coal mines can be identified via the rerefinement and classification of disaster-causing factors (DCFs) in coal mines. The study of the disaster-causing mechanism of accidents from the perspective of HDCFs in coal mines could be helpful to analyze the accident occurrence process from a new perspective, and new ideas for accident prevention and control could then be proposed. To clarify the disaster-causing mechanism of HDCFs of major and extraordinarily serious gas explosion accidents (MESGEAs) in coal mine goafs, 32 MESGEAs in coal mine goafs in China from 2000 to 2021 were adopted as a data source. By redefining the definition, connotation and characteristics of HDCFs in coal mines, 10 HDCFs were identified. Consequently, an improved decision-making trial and evaluation laboratory (DEMATEL)-interpretive structural model (ISM)-matrix of cross impact multiplications applied to classification (MICMAC) model was used to comprehensively analyze HDCFs in 3 aspects, including the centrality and cause degrees, hierarchical structure, and driving and dependence powers, from a completely objective perspective. The results demonstrated that (1) the considered MESGEAs in coal mine goafs were caused by DCFs in the management aspect by affecting the DCFs in the 3 aspects of human factors, equipment and environment, as well as under the combined effect of DCFs internal interaction contained in itself. (2) There were 2 types of disaster-causing mechanisms of HDCFs of MESGEAs in coal mine goafs: (a) the indirect disaster-causing by HDCFs in the management aspect and (b) the random coupling disaster-causing by HDCFs in human factors, equipment and environment 3 aspects.