顶板“人造解放层”防治冲击地压方法、机理及应用

The method, mechanism and application of preventing rock burst by artificial liberation layer of roof

  • 摘要: 冲击地压矿井开展解放层(保护层)开采,能够根本性的改造采掘工作面应力集中程度,从而大范围降低采掘活动空间冲击危险性。针对无解放层可采的单一煤层矿井,为了实现冲击地压煤层区域性卸压目标,提出了煤层上覆主导致灾层位厚硬顶板区域水力压裂“人造解放层”卸压防治冲击地压方法,并建立了工程力学模型,综合采用理论分析、工程验证等方法进行区域性卸压机理及工程试验研究。结果表明,在冲击地压发生载荷供给历程中,通过区域性改造煤层上覆岩层结构与载荷,可以改变冲击地压发生必须的基础静载荷集聚;针对顶板控制型冲击地压矿井,在开拓、准备、回采不同阶段,针对影响冲击地压发生的厚硬顶板开展区域性水力压裂改造覆岩结构与载荷分布,使得巷道掘进及工作面回采期间均处于压裂覆盖范围下的低应力区,实现冲击地压单一煤层顶板产生“人造解放层”效应;顶板区域水力压裂人造解放层卸压防治冲击地压机理为:与压裂前相比,煤层上覆厚硬顶板人为区域性致裂,在走向上使其长梁变短梁,大块变小块,从而不具备大面积悬臂功能,降低由悬空面积增大的顶板断裂带来的动载荷;在倾向方向上也使得其上覆载荷由硬传递变为软传递,降低了压裂区域下方煤层的整体静载水平;在陕西孟村煤矿401102综放工作面首次进行地面区域压裂“人造解放层”技术试验后,工作面回采期间微震事件呈现高频低能分布,顶板岩层断裂块度减小,顶板水均匀降落在采空区,工作面涌水量降低,采场及两巷压力及变形量降低显著,实现了解放层卸压效果。

     

    Abstract: The development of free layer(protective layer)mining in rockburst mines can fundamentally improve the stress concentration of mining face, and thus reduce the impact risk of mining activities in a large space. In order to achieve the regional pressure relief goal of a single coal seam with rockburst tendency that can be mined without a liberated layer, a method of “artificial liberated layer” for the pressure relief and prevention of rockburst in the thick and hard roof area of the main disaster zone above the coal seam created by hydraulic fracturing is put forward. The engineering mechanical model is established, and the regional pressure relief mechanism and engineering test research are comprehensively carried out by using theoretical analysis, engineering acceptance and other methods. The results show that in the load supply process of rockburst, the foundation static load concentration necessary for rockburst can be changed by the regional transformation of the structure and load of overlying strata of coal seam. For the roof controlled rockburst mines, in the different stages of development, preparation and mining, a regional hydraulic fracturing is carried out for the thick and hard roof, that affects the occurrence of rockburst, to transform the overburden structure and load distribution. Therefore, the roadway excavation and mining face are in the low stress area under the fracturing coverage, and the effect of “artificial liberation layer” is realized for mining a single coal seam under rockburst threat. The mechanism of hydraulic fracturing in the roof area to relieve pressure and prevent rock burst is that compared with that before fracturing, the thick hard roof plate overlying the coal seam is artificially fractured regionally, making its long beams become short beams and large blocks become small blocks in the strike, so it does not have the function of large-area cantilever and reduces the dynamic load brought by the roof fracture caused by the increase of suspended overburden volume. In the inclined direction, the overburden load changes from hard transmission to soft transmission, reducing the overall static load level of the coal seam under the fracturing area. The first surface regional fracturing test for creating an “artificial liberated layer” was carried out in No.401102 fully mechanized caving face at the Mengcun Coal Mine in China. After the fracturing operation, the micro-seismic events during mining presented a high-frequency and low-energy distribution, the fracture fragmentation of roof rock was reduced, the roof water fell evenly in the goaf, the water inflow of the working face was reduced, the pressure and deformation of the working face and two roadways were significantly reduced, and the pressure relief effect of the liberated layer was achieved.

     

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