| Stress-relief mining which is divided into ascending stress-relief mining and descending stress-relief mining has become one of the effective methods of high gas outburst coal seams mining safety and gas extraction. In the process of ascending pressure-relief mining, overlying rock relief area and the scope of gas extraction are related to the roof strata caving, interlayer rock physical properties, length of working face, mining thickness and gas pressure and content, etc. In this paper, evolution of overburden rock breaking and characteristics of stress relief are mainly studied when there are the varying amounts of hard and thick strata in the process of ascending order pressure-relief mining.According to the occurrence features, physical and mechanical characteristics and features of mining technology of coal A3, the evolution characteristics of hard-and-thick strata breakage and relief effects for coal B4in ascending order pressure-relief mining are studied in this paper by field test, numerical simulation analysis, similar simulation material test analysis and the research method combining theory with analysis.The feasibility of ascending mining in A3coal seam is determined by theoretical analysis and calculation according to the occurrence characteristics and physical and mechanical properties of overlying coal rock being obtained in the field sampling and laboratory tests. The breakage characteristics of hard-and-thick strata and its influence law on the evolution of overburden rock stress, displacement and fractures are researched by UDEC2D numerical simulation models and laboratory experiments similar material simulation models which are established to study A3coal mining protecting B4coal in the conditions under different combinations of rock. The evolution characteristics of hard-and-thick strata breakage and stress-releasing effect in ascending order mining are obtained according to experimental data analysis. |
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