Damage evolution law of multi-hole blasting igneous rock and quantitative evaluation model of damage degree based on fractal theory and clustering algorithm.

The geological phenomenon of igneous rock invading coal seam is widely distributed, which induces mining risk and affects efficient mining. The pre-splitting blasting method of igneous rock is feasible but difficult to implement accurately, resulting in unnecessary safety and environmental pollution risks. In this paper, the blasting model with penetrating structural plane and the multi-hole blasting model with different hole spacing were established based on the Riedel-Hiermaier-Thoma (RHT) damage constitutive to explore the stress wave propagation law under detonation. The damage cloud diagram and damage degree algorithm were used to quantitatively describe the spatio-temporal evolution of blasting damage. The results show that the explosion stress wave presents a significant reflection stretching effect under the action of the structural plane, which can effectively aggravate the presplitting blasting degree of the rock mass inside the structural plane. The damage range of rock mass is synchronously evolved with the change of blasting hole spacing. The blasting in the igneous rock intrusion area of the 21,914 working face is taken as an application example, and the damage degree of rock mass is reasonably evaluated by the box-counting dimension and K-means clustering method, which proves the effectiveness of the blasting scheme and provides reference value for the implementation of related blasting projects.

Utilization of broken rock in shallow gobs for mitigating mining-induced water inrush disaster risks and environmental damage: Experimental study and permeability model.

Coal mining-induced groundwater losses may trigger water inrush disasters and surface ecological degradation. The compaction and seepage characteristics of broken rock in gobs can be used to find the balance point of water inrush prevention and water resource protection in shallow coal seam groups. These characteristics, as well as geological and engineering parameters of shallow coal seam mining, are experimentally determined in this study. The performed permeability tests revealed that the percentage of voids in broken rock exponentially decreased with the axial stress. The water seepage of broken rock in the compaction process conformed to the Forchheimer theory, with the permeability ranging from 10-1 to 10 D. The initial value and reduction range of mudstone permeability in the three lithologic samples were the smallest. The uniaxial compression strength reduction caused by the increase in unit mass water due to water saturation of natural rock samples were 5.8 and 3.2 % for coal and sandstone, respectively. Based on the experimental results on compaction and seepage of broken rock, the axial stress-percentage of voids-permeability model considering compaction and re-crushing was established. The mudstone roof was found to be the key rock stratum during re-mining for ecological protection and hydraulic connection evaluation of the overburden.

Distribution Characteristic and Migration Mechanism of Toxic Gases in Goafs during Close-Distance Coal Seam Mining: a Case Study of Shaping Coal Mine.

It is imperative to have an in-depth understanding of the gas migration mechanism during close-distance coal seam mining, not only to prevent fires in the coal industry but also to propose safety strategies for controlling toxic gases. The 1818 working face of the Shaping Coal Mine was used as an exemplary close-distance coal seam mine. Through the construction of boreholes and the arrangement of bundle pipes in the two parallel grooves of the working face and the upper goaf at the corresponding positions in the working face, the gases in the upper and lower goafs were monitored online timely. The firsthand information about the gas distribution was obtained through on-site tests, which provided the robust data for studying the migration mechanism of toxic gases during close-distance coal seam mining. By studying the spatial distribution of harmful gases in the upper goaf without mining the overlying coal, the static distribution law of gas was obtained. By discussing the spatial distribution and migration of harmful gases in the goaf of the overlying coal seam during mining, the dynamic distribution law of the gas was obtained. By studying the spatial distribution and migration of toxic gases in the mined-out area of the lower coal seam during mining, the dynamic distribution of gases in the mined-out area of the lower coal seam was obtained. Moreover, the migration mechanism of gas emission from the goafs in the close-distance coal seam was explored. By analyzing the factors responsible for the accumulation of toxic gases in the return air corner, feasible safety measures were also proposed to prevent this hazard during close-distance coal seam mining.