动静载下深井临空巷道冲击破坏分析及防治

Analysis and prevention of impact damage in deep goaf roadway under dynamic and static load

现有针对临空巷道冲击地压的研究主要集中在静载致灾方面,对静载基础上的动载叠加致灾机制研究不够,在巷道围岩动载应力波响应方面未能将巷道破坏方式同应力波扰动及其力学效果相联系。针对该问题,以内蒙古鄂尔多斯矿区某矿3-1103工作面临空巷道为研究对象,分析了临空巷道冲击破坏特征和冲击地压发生的动静载荷源:临空巷道处于采空区侧“F”型覆岩结构下,静载荷源为侧向集中支承应力和工作面回采超前采动集中支承应力的叠加应力场;动载荷源为基本顶的初次来压、周期来压和见方破断形成的近场矿震以及远场矿震释放能量,在冲击性顶板岩层下动静载组合效应极易诱发高地应力下应力场差异且应力集中的巷道产生冲击灾害。采用FLAC3D数值模拟方法分析了临空巷道动静载荷源下冲击巷道所处的应力状态以及矿震应力波致灾影响作用,并与现场冲击破坏特征进行对比验证分析。数值模拟结果与现场破坏特征具有较强一致性,在采空区压实过程中,最大垂直集中应力由煤柱上方转移至巷道回采帮侧,锚杆轴力呈现不对称分布状态;动载过程中,巷道围岩主应力差重复加卸载,迎波侧应力波最大质点振动速度(PPV)值大于背波侧,围岩浅部应力波反射叠加,PPV值大小与围岩浅部动载后最大位移量一致;临空巷道围岩在动静载作用过程中形成了巷道回采帮侧与煤柱帮应力场差异以及动载应力场差异。根据动静载荷下临空巷道破坏特征及其数值模拟验证分析结果制定了静载荷卸压降载、动载荷减震消能的分源防治措施,即顶板水压致裂、顶底板爆破卸压、巷帮大直径钻孔卸压以及巷道围岩加固等措施,以达到防止厚硬顶板弹性能积聚、消弱应力波幅值以及改善围岩受力环境的目的。采取卸压措施后,实测微震以小能级、多频次的形式释放能量,微震总能量比卸压前降低了49.2%,103 J以下微震小能量事件占比由卸压前的75%升高到89%,现场巷道围岩静载降低,动静载叠加时未出现应力突变,证明了冲击防治措施的有效性。

The existing research on rock bursts in goaf roadway mainly focuses on the static load caused disaster.However,there is few research on the dynamic load superimposed disaster mechanisms based on static load.In terms of the dynamic load stress wave response of the surrounding rock of the roadway,the damage mode of the roadway is not related with the stress wave disturbance and its mechanical effects.In order to solve this problem,taking 3-1103 working face in Ordos mining area,Inner Mongolia as the research object,the study analyzes the impact damage characteristics of the goaf roadway and the dynamic and static load sources of the rock burst.The goaf roadway is under the'F'type overburden rock structure on the side of the goaf,and the source of static load is the superimposed stress field of the lateral concentrated support stress and the advanced mining concentrated support stress of the working face.The source of dynamic load is the initial pressure of the basic roof,periodic pressure and the near-field mine earthquake formed by the square area break and the far-field mine seismic release energy.The combined effect of dynamic and static load under the impact roof rock layer can easily induce impact disaster in roadways with different stress fields under high ground stress and stress concentration.The FLAC3D numerical simulation method is used to analyze the stress state of the impact roadway under the dynamic and static load sources of the goaf roadway and the impact of the stress wave of the mine earthquake,and to verify and analyze the field impact damage characteristics in comparison.The numerical simulation results have a strong consistency with the field damage characteristics.During the goaf compaction process,the maximum vertical concentrated stress is transferred from the coal pillar to the side of the roadway side,and the bolt axial force shows an asymmetrical distribution state.During the dynamic load process,the principle stress difference of the roadway surrounding rock is repeatedly loaded and unloaded,the peak particle velocity(PPV)value of the stress wave on the front wave side is larger than that on the back wave side.The shallow stress wave of surrounding rock is reflected and superimposed,the PPV value is consistent with the maximum displacement of the shallow part of the surrounding rock after dynamic load.The surrounding rock of the goaf roadway forms the difference in stress field between the side of the roadway and the coal pillar side as well as the difference in dynamic load stress field in the process of dynamic and static load.According to the damage characteristics of goaf roadway under dynamic and static load and the results of its numerical simulation and validation analysis,the separate source prevention and control measures of static load decompression and load reduction,dynamic load earthquake reduction and energy dissipation are formulated.The measures are roof hydraulic fracturing,roof and floor blasting decompression,decompression of large-diameter boreholes of roadway and reinforcement of roadway surrounding rock.These measures are used to prevent the accumulation of elastic energy of thick and hard roof,weaken the amplitude of stress wave,and improve the surrounding rock stress environment.After taking pressure relief measures,the measured microseismic energy is released in the form of small energy level and multiple frequency.The total microseismic energy is reduced by 49.2%compared with that before pressure relief,the proportion of microseismic small energy events below 103 J increases from 75%before pressure relief to 89%,the static load of the field roadway surrounding rock is reduced,and there was no sudden change of stress when dynamic and static load are superimposed,which has proved the effectiveness of impact prevention and control measures.