Control Of Dynamic Disaster In Extra Thick Coal Seams Under Complex Conditions

Dynamic disasters (rockburst, mine earthquake, mine water inrush, gas and coal outburst) occurring in extra thick coal seams under complicated geological conditions (upper coal pillar, fault structure, compound condition of hard roof and the strata containing water) have been highly threatening mine safety production. This paper studied occurring mechanism of dynastic disasters and treatment techniques through in-situ testing, case analysis, theoretical research, lab test and reproduction practice based on three typical dynamic disasters induced by upper coal pillar, fault structure, compound condition of hard roof and the strata containing water, respectively in Junde Coal Mine and Fuli Coal Mine in Hegang Mining Area and Guotun Coal Mine in Juye Mining Area. The main results are as follows:(1) "Burst-danger area" which takes stress as criterion exists in lower coal seams in the rock stress-transfer scope of multi-seam mining space. Estimation models of Stress-influence area" and rockburst danger criterion are established. The estimation models contain calculation models of upper coal pillars in trend and dip directions and the determination method of the"burst-danger area" according to the ratio of vertical stress to coal uniaxial compressive strength.(2) The "B-S-B" dynamic model for rockburst occurrence process in layered longwall panels within extra thick coal seams is established, and the occurring mechanism of slip burst in layered longwall panels within extra thick coal seams after buckling failure of floor coal is clarified. "B" means buckling failure occurs in floor coal. "S-B" means sliding burst in lower floor coal. Buckling failure occurs in floor coal under the action of horizontal stress component. When the range of buckling failure is large, the first rockburst (Buckling Burst) may occur in floor coal. Plastic slip occurs in lower floor under the action of horizontal stress component and vertical stress component. When the range of plastic slip reaches the scale of structural instability of lower floor, the second rockburst (Sliding Burst) occurs in lower floor. The "B-S-B" dynamic model can provide theoretical basis for engineering problems such as rockburst danger comparison and mining technology selection between sub-level caving mining and slice mining in extra thick coal seams, tunnel surrounding rock control, advanced support design, as well as rockburst prevention and design.(3) Rockburst mechanism of structural isolated long wall panels is proposed. The basic reason why the dynamic phenomenon occurs when the mining face is several hundred meters away from the fault plane is studied. The fault plane is inclined to the direction of the coal wall and intersects with the fracture line of overlying strata, which leads to the formation of "space isolated coal pillar". Therefore, stress concentration between fault plane and mining face results in rockburst of structural isolated long wall panels. The average stress estimation formulae of the coal from working face to fault face are built and the danger criterion of rockburst is established.(4) The compound dynamic disaster of "rockburst and water inrush" mechanism is clarified. The sudden increase of stress in surrounding rock near the coal wall caused by the regular fracture of hard roofs leads to the increase in fractural range in surrounding rock, and thus induces the compound roof movement dynamic disaster of "water inrush"; Draining in the independent hydro-geologic area or water-rich area (which is equal to small-sized mining) leads to the local stress concentration, and thus induces compound dynamic disasters of "rockburst induced by draining". This kind of compound dynamic disaster is more obvious in extra thick coal mines because of the characteristics of "high elasticity, large mining height, strong energy release, low strength, easy failure, and great failure depth".(5) The reproduction technical system after rockburst accidents is proposed. In order to prevent the re-occurring of rockburst accidents during production, the reproduction safety technical standards and corresponding technical systems after rockburst accidents are proposed. The technical system has been successfully applied and tested in 3·15 accident long wall panel in Junde Coal Mine, which can provide experience for production in rockburst accident long wall panels under similar conditions.The investigation result has been applied in Junde Coal Mine and Fuli Coal Mine in Hegang Mining Area and Guotun Coal Mine in Juye Mining Area, which achieved considerable economic and social effectiveness.