特厚煤层低位双硬顶板破断失稳规律试验研究

Experimental Study on Fracture and Instability Law of Lower Double Hard Roof in Extra-Thick Coal Seam

针对特厚煤层双硬顶板放顶煤开采覆岩冲击性破断问题以及宽煤柱沿空巷道变形较大、护巷困难、需反复刷扩等问题,以麻家梁矿14202工作面为工程背景,通过物理相似模拟试验,对特厚煤层低位双硬顶板结构破断的动载效应进行研究分析。结果表明:下位坚硬顶板自离层萌生到全部垮落工作面累计推进36m,推进60m时发生初次失稳破断,垮落厚度为4.2m,破断角为60°,顶板断裂线距煤壁5.8m,周期垮落步距约为23~25m;上位坚硬顶板自下分层垮落到完全垮落工作面累计推进23m,破断步距约为55~65m,破断角与上位坚硬顶板一致;位移监测结果显示,下位坚硬顶板与软弱夹层中下部分、上位坚硬顶板与软弱夹层上分层以及其上覆软弱岩层运动规律保持一致;双硬顶板破断失稳在采空区侧形成一定范围的应力升高区,应力峰值为23MPa,应力集中系数为1.57,应力峰值距影响范围为20m;下位坚硬顶板破断形成“短悬臂梁”结构,该结构随工作面回采动态前移形成小周期来压,上位硬顶破断形成“长砌体梁”结构,该结构破断失稳动载作用于下部“短悬臂梁”,使得其提前破断而共同作用于工作面支护体,形成大周期来压。研究结果可为特厚煤层开采多层硬顶条件下的围岩控制提供理论依据。

Aiming at the problems of overburden rock impact fracture in top coal caving mining with double hard roof in extrathick coal seam,as well as large deformation of wide coal pillar gob-side entry,difficulties in roadway protection and repeated brushing and expansion,taking 14202working face of Majialiang Coal Mine as the engineering background,through physical similarity simulation experiment,the dynamic load effect of lower double hard roof structure fracture in extra-thick coal seam was studied and analyzed.The results show that the lower hard roof has accumulated a total advance of 36mfrom the initiation of the detachment layer to the complete caving of the working face,and the first fracture and instability occurs when the advance is 60m.The caving thickness is 4.2m,the fracture angle is 60°,the roof fracture line is 5.8mfrom the coal wall,and the periodic caving step is about 2325m.The cumulative advance of the upper hard roof from the lower layer to the fully caving of the working face,advancing a total of 23m,the fracture step is about 5565m,and the fracture angle is consistent with the lower hard roof.The displacement monitoring results show that the motion law of the lower hard roof and the middlelower part of the weak interlayer,as well as the upper hard roof and the upper layer of the weak interlayer and the overlying weak rock layer are consistent.The fracture and instability of the double hard roof forms a certain range of stress rise zone on the side of the goaf.The peak stress is 23MPa,the stress concentration factor is 1.57,and the influence range of the peak stress is 20m.The lower hard roof fractures form a“short cantilever beam”structure,which forms a small periodic weighting with the dynamic forward movement of the working face.The upper hard roof fractures form a“long masonry beam”structure,and the dynamic load of fracture and instability acts on the lower“short cantilever beam”,so that it breaks in advance and acts together on the working face support to form a large periodic weighting.The research results can provide a theoretical basis for surrounding rock control under the condition of multi-layer hard roof in extra-thick coal seam mining.