Abstract
Determining a reasonable barrier pillar along gob-side entry of spontaneous combustion coal seam is of great significance to the prevention of spontaneous combustion. In this paper, considering the actual situation of 4301 and 4302 working faces of II-class spontaneous combustion coal seam in Changheng Mine, the characteristics of rock mass collapse and mining-induced stress redistribution of barrier pillar and adjacent area were analyzed, the cusp catastrophe model of coal pillar instability and the theoretical model of limit width of coal pillar air leakage spontaneous combustion were established, and a measurement scheme of side abutment pressure in 4301 working face was carried out. The theoretical model of the coal pillar along the gob-side entry shows that its instability is related to density of overlying strata, physical and mechanical parameters of coal body, dip angle of coal seam and weak face, and buried depth and mining width of working face. And the coal pillar in 4302 working face will be unstable if the width a ≤ 6.8 m . Field measured data shows that 2-8 m is the stress-relaxation area of side solid coal. Then, the width of coal pillar was determined as 7 m. The maximum displacement of rib-to-rib and roof-to-floor of 4302 tailentry was 520 mm and 280 mm, respectively. The coal spontaneous combustion (CSC) observation monitoring results showed that the carbon monoxide volume fraction was in the normal range during the entire process of mining, and no other signs of gas were found. The research results can provide a reference for the barrier pillar designing in the mines under similar conditions.
Highlights
China is the world’s largest producer and consumer of coal, accounting for more than 56.8% of its primary energy consumption
Calculation Results of Narrow Coal Pillar Theoretical Model. It can be seen from Equation (15) that the instability of coal pillar in gob-side entry is related to the stiffness of plastic failure area and the stiffness ratio of stable elastic core area
It is related to density of overlying strata, physical and mechanical parameters of coal pillar, dip angle of coal seam and weak face, and buried depth and mining width of working face
Summary
China is the world’s largest producer and consumer of coal, accounting for more than 56.8% of its primary energy consumption. On the determination of the width of barrier pillar, many scholars and engineers have carried out a lot of research by means of field measurement, statistics, theoretical calculation, and numerical simulation and put forward lots of effective design methods. Xu et al [18] studied the width of coal pillar along the gob-side entry in the isolated working face of the soft coal seam through numerical simulation and monitored the stability of the surrounding rock of the entry with a small coal pillar of 5 m. Based on the engineering background of narrow barrier pillar in LTCC working face of II-level spontaneous combustion coal seam, using the comprehensive research methods of mechanical modeling and field measurement, this paper discusses the determination method of the optimal narrow coal pillar width to prevent sudden instability and spontaneous combustion of coal pillar. The research results can provide reference for the design of barrier pillar in coal face under similar conditions
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