采动覆岩裂隙与渗流分形演化规律及工程应用

Fractal evolution law of overlying rock fracture and seepage caused by mining and its engineering application

高瓦斯煤层开采过程中,采动覆岩裂隙与渗透演化规律对卸压瓦斯运移及分区富集具有控制作用,因此如何定量化精准描述采动覆岩裂隙发育及渗透率分布特征是提高采空区及裂隙带瓦斯抽采效率的关键。本文以阳泉矿区平舒煤矿为工程背景,模拟工作面开采过程中覆岩移动变形与裂隙动态演化规律,引入分形几何理论定量描述采动覆岩裂隙产生和发育过程,进而推导裂隙岩体的分形渗透率模型,实现了覆岩裂隙瓦斯运移优势通道及渗透率非均匀分布规律的精细表征。研究表明:随着工作面的不断推进,采动覆岩裂隙不断向前向上发育,覆岩裂隙发育总体表现为采空区两侧高度发育,中部压实的“双峰”状分布规律;采空区两侧的竖向破断裂隙区分形维数分别达到1.143,1.151,明显大于其他区域,是采动裂隙充分发育区和卸压瓦斯运移优势通道;根据裂隙岩体的分形渗透率模型,计算得到垮落带渗透率为1×10^(-5)~4×10^(-5)m^(2),裂隙带渗透率为8.9×10^(-9)~9.8×10-7m^(2);覆岩裂隙带内渗透率分布存在明显分区现象,总体呈现两侧高、中间低的“马鞍形”特征,高渗透区域主要集中于近工作面侧采空区(沿走向长度0~30 m)以及近开切眼侧采空区(沿走向长度110~150 m)的范围内,高渗透率区域的垂向上限可以达到煤层以上35 m;基于此提出试验工作面高、低位抽采巷道的技术参数并进行应用,取得了良好的采空区及裂隙带卸压瓦斯抽采效果。该研究对推动采动覆岩裂隙与渗流演化规律从理论到实践的应用具有重要的参考价值。

During the mining process of high gassy coal seam,the fracture and permeability evolution law of mining overburden rock has a control effect on the pressure relief gas migration and partition enrichment.Therefore,how to quantitatively and accurately describe the fracture development and permeability distribution characteristics of mining overburden rock is the key to improve the gas drainage efficiency of goaf and fracture zone.Based on the engineering background of Pingshu Coal Mine in the Yangquan Mining Area,this paper simulates the movement and deformation of overlying strata and the dynamic evolution law of fractures during the mining process of the working face.The fractal geometry theory is introduced to quantitatively describe the generation and development process of mining-induced overburden fractures,and then the fractal permeability model of fractured rock mass is derived.The fine characterization of the dominant channel of gas migration and the non-uniform distribution of permeability in overburden fractures is realized.The research shows that,with the continuous advancement of the working face,the overburden fissures develop forward and upward,and the overall development of the overlying fissures is a“double-peak”distribution pattern of high development on both sides of the goaf and compaction in the middle.The distinguishing dimension of vertical fractures on both sides of goaf reaches 1.143 and 1.151respectively,which is obviously larger than that of other areas.It is the fully developed area of mining fracture and the dominant channel of pressure relief gas migration.According to the fractal permeability model of fractured rock mass,the permeability of the collapse zone is calculated to be 1×10^(-5)–4×10^(-5)m~2,and the permeability of the fracture zone is 8.9×10^(-9)–9.8×10-7m~2.The permeability distribution in the overlying fissure zone has an obvious zoning phenomenon,generally showing a“saddle-shaped”feature with high sides and low middle.The high permeability area is mainly concentrated in the goaf near the working face side(length 0–30 m along the strike)and the goaf near the incision side(length 110–150 m along the strike).The upper limit of the vertical high permeability area can reach 35 m above the coal seam.Based on this,the technical parameters of the high and low-level drainage tunnels in the experimental working face are put forward and applied,and good gas drainage effects of pressure relief in the goaf and fracture zone have been obtained.This research has important reference value to promote the application of the evolution law of overburden fissures and seepage from theory to practice.