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This study investigates the effect of key stratum on the mining abutment pressure of a coal seam. Firstly, a total of 42 configurations with different key stratum thicknesses and heights have been numerically simulated by the Universal Distinct Element Code (UDEC) software. Then, through the analysis of two sets of parameters derived from the simulation results, the peak abutment pressure and the range of influence, shows that the effect of key stratum on the abutment pressure is conditional. For a relatively small key stratum thickness, less than 159 m, the effect on the abutment pressure is negligible unless the key stratum height is higher than the critical height of 421 m. On the other hand, for the key stratum thickness bigger than 159 m, the abutment pressure is affected irrespective of the key stratum height. Finally, in order to verify the simulation results, the abutment pressure of a field model has been analyzed. The analysis shows that the abutment pressure of the field model with a key stratum is 42% higher than that of the model without any key stratum. The stress at the field model has increased from the virgin stress of 14.6 MPa to the stress of 21.5 MPa. Meanwhile, the stress concentration coefficient has changed from 1 to 1.5, which caused the coal and gas burst disaster. The results of this study can be very useful to explain the reason for the occurrence of some dynamic disasters affected by the key stratum. [ABSTRACT FROM AUTHOR]

In order to effectively control gas unbalance phenomenon of gas occurrence in coal mine, this paper put forward the concept of gas enrichment area and gave the general characteristics of gas enrichment area. Based on geological condition in Zhaogu No. 1 Coal Mine, the paper discussed the gas geological features and analyzed the formation mechanism of gas enrichment area in the thick loess-thin bedrock coal seam, and then obtained the recognition method of gas enrichment area by the overlying bedrock characteristic of coal seam. On the basis of which, the gas enrichment area of Zhaogu No. 1 Coal Mine was confirmed, that was the bedrock layer thickness greater than 50 m and coal seam overlying bedrock gradient greater than 0. 06 or the bedrock layer thickness greater than 150 m area. Coal mining practice verified gas enrichment area identification and actual gas occurrence consistency. [ABSTRACT FROM AUTHOR]

Abstract: Underground coal fires pose a threat to the environment and the health of those living in their proximity and can result in economic losses if these fires occur at mining areas. Design of methods to extinguish these fires requires that the extent of the subsurface fire be delineated. A conceptual picture of the workings of a subsurface coal fire near Durango, CO is presented first, which shows how the overburden above the burning coal seam can become heated. In high temperature and low O2 conditions, the heating of the overburden leads to the formation of magnetite, and its presence and the alignment of magnetic moments can be detected by a magnetometer. Magnetometer surveys allow high resolution areal mapping that differentiates among previously burned, currently burning, and unburned coal seam areas. The current and previous locations of the subsurface fire regions that are delineated by the magnetometer survey conducted at a fire on the Southern Ute Indian Reservation are consistent with various supporting data such as gas composition, temperature, and snowmelt data. [Copyright &y& Elsevier]