厚硬顶板覆岩冲击矿震影响的远近场效应研究

Investigation on the near-far field effect of rock burst subject to the breakage of thick and hard overburden

针对厚硬顶板覆岩破断释放冲击能量影响采场安全性等问题,基于材料力学及冲击动力学,建立了冲击震源层破断力学模型,研究了覆岩冲击震源层初次破断和周期破断产生的冲击能量大小以及冲击震动波在传播过程中的能量耗散机理,分析了厚硬顶板覆岩冲击震源层位能级对下伏采掘空间冲击矿震影响的远近场效应。研究发现:冲击震源层破裂释放能量与采高、冲击震源层破裂尺度、冲击震源层初次破断步距以及周期破断步距呈正比,与冲击震源层的层位高度成反比。冲击震动波能量随传播距离增大呈幂指数降低,且不同岩性对冲击能量的耗散能力不同。动载冲击波的作用时间分为冲击压缩区、动荡反射区及能量衰减区,下伏采掘空间围岩质点震动速度随冲击震源层位距离增大呈指数型衰减,随冲击震动能量的增大呈指数型增大,采掘空间上方厚硬顶板,均存在一临界冲击能量和临界冲击距离,近场的小能量不一定发生弱冲击,远场的大能量也不一定发生强冲击,冲击灾害程度主要取决于能量与距离的比值。采用能距比§来近似描述这种影响效应,通过典型冲击事件统计分析发现:当能距比§∈(0~10^(2))无冲击,§∈(10^(2)~10^(3))弱冲击,§∈(10^(3)~10^(4))中等冲击,§∈(10^(4)及以上)强冲击。厚硬顶板覆岩层位对矿井冲击矿震影响具有显著的远近场效应,分别会带来采面、采区、矿井、矿区不同区域不同程度的冲击地压显现甚至矿震等灾害,厚硬顶板覆岩层位的存在也为冲击矿震防治提供了靶点部位,可采取地面-井下高低位立体协同对向压裂破岩释能从源头防冲。

The breakage of thick and hard overburden strata are generally associated with the suddenly release of the impact energy,threating the safe mining of underground coal seam.The fracture mechanics model of shock source layer was firstly established,on the basis of materials-and impact-mechanics.The value of the impact energy released during the first and periodic fracture of shock source layer and the energy dissipation mechanism of the shock wave within this process were then evaluated,followed by the analysis of the near-and far-field effects of rock burst attributed to the breakage of the thick and hard overburden on the driving and excavation of the underlying strata.It is apparent that the released energy is directly proportional to the mining height,the scale of the shock source layer breakage,the initial-and the periodic breakage of the shock source layer.Whereas,it is inversely proportional to the distance apart from the shock source layer.The energy of the shock wave decreases exponentially with the increase of propagation distance and the dissipation capacity of shock energy is sensitive to the lithology.In addition,the action time of dynamic shock are classified into the shock compression zone,turbulent reflection zone and energy attenuation zone.The particle vibration velocity of surrounding rock in the underlying mining space decreases exponentially with the increase of the distance from the shock source layer,while it increases exponentially with the impact vibration energy.In particular,there is a threshold value of the critical impact energy and the impact distance.That is,the weak rock burst will not be caused by the small energy in the near-field and vice versa.The serious of the impact disaster mainly depends on the ratio between the energy and distance(§).Based on the statistical analysis of typical rock burst accidents,it is indicated that:if§∈(0~10^(2)),there is no rock burst risk.When§∈(10^(2)~10^(3)),the weak impact event will be occurred.While§∈(10^(3)~10^(4))and§>10^(4),the medium and the strong impact event will be potentially occurred.Moreover,the near-and far-field of rock burst is significantly obvious for the coal seam with the thick and hard overburden strata.In this case,the potential rock burst and even the mine shock disasters will be generated in different areas such as the longwall,mining zone and mining area,respectively.Even though,the existence of thick and hard overburden strata provides a target for the prevention and controlling of rock burst.The three-dimensional collaborative fracturing method is strongly recommended to release energy,which is believed to be the initial and effective method in preventing the rock burst.