Abstract
A thin basement coal seam mining model under different overlying strata conditions was developed using the discrete element software UDEC. This approach is used to discuss the safety mining of the thin basement coal seams. Fracture development in overlying and rock strata movement law in the stope was discussed. The relationship between support and surrounding rocks under different overlying strata conditions was analyzed. Lastly, a field industrial test was conducted based on the research results. A few major conclusions could be drawn. Under load transmission in loose water-bearing strata, causing a large-scaled rock strata movement to advance into the working face is easy when only one bearing stratum exists in the overlying strata. Meanwhile, the support bears strong loads, which can easily be collapsed. When two bearing strata exist in the overlying one, the upper bearing stratum can form a voussoir beam structure. Loads on the support decreased substantially compared with those under single bearing stratum, whilst the probability of pressing frame was reduced accordingly. A weathered zone above the stope was reinforced by ground J-type drilling pregrouting, thereby improving the physical and mechanical properties and increasing the bearing capacity of the rock strata in the grouting range and safety mining of the working face in the lower coal seams. Research results provide important references for the safety mining of thin basement coal seams under similar conditions.
Highlights
Given the continuous increase of upper mining limit in mines in eastern and northern China, water and sand inrush accidents induced by mining of the working face in thin basement coal seams have become increasingly prominent in recent years [1]
Mining in special geological conditions, such as thick loose water-bearing stratum and thin basement, continuously face a series of problems, which attributes to hydrogeological differences in various regions, water abundance in loose stratum, and increased upper mining limit
Causing crushed hydraulic support on the working face when only one bearing stratum exists in the overlying strata is easy. e preceding research conclusions and previous engineering experiences indicated that a thin basement coal seam mining test should be performed by creating a high bearing stratum in the weathered zone through artificial pregrouting
Summary
Given the continuous increase of upper mining limit in mines in eastern and northern China, water and sand inrush accidents induced by mining of the working face in thin basement coal seams have become increasingly prominent in recent years [1]. E models were used to simulate fracture development and movement laws in the overlying strata after mining of the working face. E fracture development in the overlying and rock strata movement laws when single and double bearing layers exist in the working face is shown in Figures 3 and 4, respectively. E fracture in the rock strata above the main roof further developed as a response to the first periodic fracture of the main roof (bearing layer) when the advancing distance in the working face was 40 m (see Figure 3). Is condition resulted in a large-scale subsidence of rock strata above the main roof Under this circumstance, causing crushed hydraulic support in the working face is easy [14]. Fractures began to develop in the overlying rocks above the main roof (low bearing strata) when the advancing distance was 45 m (see Figure 4). Causing crushed hydraulic support on the working face when only one bearing stratum exists in the overlying strata is easy. e preceding research conclusions and previous engineering experiences indicated that a thin basement coal seam mining test should be performed by creating a high bearing stratum in the weathered zone through artificial pregrouting
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