Solutions for the maintenance of safety in an isolated working face has not been well achieved; this is attributed to its unique overburden structure and the strong mining-induced stress during the advancement. This paper is devoted to filling this research gap and is based on the case study of LW 10304 in the Xinglongzhuang Coal Mine, in China. The overburden structure and stress distribution characteristics of this isolated working face were theoretically investigated, followed by the development of a comprehensive identification method. The research results showed the following: (1) The overburden strata of LW 10304 is in the form of a short “T” shape and the stress increment is featured with the overall “saddle” shape before the extraction of the isolated working face. During this period, the lower key strata and main key strata affect the stress level at the two ends and the central part of the working face, respectively; (2) Both the frequency and energy of micro-earthquakes in the working face account for more than 95%, which is positively correlated with roof damage and rib spalling, associated with some overlaps between the damaged zones; (3) The fracture movement of inferior key strata near the coal seam plays a dominant role in affecting microseism activity and mining-induced stress. The microseism energy attributed to roof breakage accounts for 43.34% of the overall energy; (4) A comprehensive indexing system, covering microseism frequency, microseism energy, and support resistance, was established to identify the mining-induced stress intensity of the isolated working face. The early warning efficiency of the “strong” degree of mining-induced stress is 0.94, which is believed to provide an option for other isolated working faces with similar geological and mining conditions.
Based on the mining and geological conditions in No.12 Mining District of Jining No.3 Coal Mine, the variation laws of stress and deformation of the lower-protected seam along with the mining operation of upper-protective seam are studied by numerical simulation and field test in this paper. The results show that the distribution of in situ stress in protected seam is changed correspondingly during the protective seam mining. While mining the protected seam, the vertical stresses around the protected seam experienced three stages: stress increasing before mining, decreasing after mining and stepwise steady stage. In addition, the protective seam mining can also cause expansive deformation in protected seam and its surrounding rock, destroy the strata structure and release the elastic energy in advance, thus reducing the rock burst risk in protected seam. The results of numerical analysis and the field monitoring results are basically in agreement. The study in this paper will provide theoretical basis and practical value for reasonable design and safety mining of coal seams with rock burst propensity.
An investigation of risk factors has been identified as a crucial aspect of the routine management of rockburst. However, the identification methods for principal impact factors and the examination of the relationship between seismic energy and other source parameters have not been extensively explored to conduct dynamic risk management. This study aims to quantify impact risk factors and discriminate hazardous high-energy seismic events. The analytic hierarchy process (AHP) and entropy weight method (EWM) are utilized to ascertain the primary control factors based on geotechnical data and nearly two months of seismic data from a longwall panel. Furthermore, the distribution law and correlation relationship among seismic source parameters are systematically analyzed. Results show that the effect of coal depth, coal seam thickness, coal dip, and mining speed covers the entire mining process, while the fault is only prominent in localized areas. There are varying degrees of log-positive correlations between seismic energy and other source parameters, and this positive correlation is more pronounced for hazardous high-energy seismic events. Utilizing the linear logarithmic relationship between seismic energy and other source parameters, along with the impact weights of dynamic risks, the comprehensive energy index for evaluating high-energy seismic events is proposed. The comprehensive energy index identification method proves to be more accurate by comparing with the high-energy seismic events based on energy criteria. The limitations and improvements of this method are also synthesized to obtaining a wide range of applications.
With the increase in coal mining depth, many rock bursts triggered by fold structures have been observed, but the disaster mechanism is not clear. This research aims at investigating the influence of upright fold structure(UFS) on rock burst mechanisms. The mechanical model and numerical model of the UFS are constructed, and the mining stress evolution law and rock burst mechanism of working face in a UFS area are studied by utilizing engineering practice. The research shows that the occurrence of rock burst disasters in the fold structure area has obvious regional characteristics. The horizontal and vertical stress of the UFS in the horizontal distribution is similar to the periodic variation characteristics of the sine (cosine) curve. The stress state of the UFS area is divided into five areas. The horizontal and vertical stress concentration factors increase first and then decrease with the working face gradually approaching and away from the upright fold syncline axis. A roadway impact risk index I0 is proposed to determine whether the roadway is damaged, and the mechanism of inducing ground pressure during mining in UFS areas of deep mines is expounded. The control plan effectively reduces the stress levels of surrounding rock in working faces.
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