特厚煤层分层综放开采上、下分层工作面斜交布置，下分层综放工作面间歇性过上分层遗留区段煤柱，覆岩破断运动及矿压显现规律复杂，影响下分层工作面安全开采。论文以甘肃华亭煤电股份有限公司砚北煤矿25023_下综放工作面为工程背景，采用数值计算、物理相似模拟、理论分析及现场实测相结合的研究方法，分析了上分层遗留煤柱下斜交工作面围岩应力变化及覆岩变形破坏规律，得出了上分层遗留区段煤柱开采时区段煤柱及下分层工作面支承压力变化规律，揭示了综放工作面过遗留煤柱覆岩结构演变特征。主要结论如下：

（1）数值计算实验上分层3个工作面开采完成后遗留2个区段煤柱最大应力峰值分别为为42.53 MPa和41.12 MPa，应力集中系数为3.24和3.35。上分层遗留区段煤柱下斜交工作面过煤柱开采过程中周期性进、出煤柱，进煤柱时下端口运输平巷最先进入煤柱，出煤柱时上端口回风平巷最后离开煤柱。在工作面进遗留区段煤柱阶段，在工作面距离煤柱45 m处时，受超前支承压力作用，运输平巷处压力峰值达到45.3 MPa，较下分层未开采时增大了13.7%；工作面出区段煤柱阶段，当工作面距离煤柱15 m处，受超前支承压力作用，回风平巷处压力峰值达到46.7 MPa，较下分层未开采时增大了9.9%。

（2）上分层遗留区段煤柱下斜交工作面过煤柱开采过程中，引起区段煤柱失稳及覆岩大尺度空间垮落，远距离的高位岩层破断后形成砌体结构，近距离的低位岩层经历了二次破断，形成“悬臂梁+砌体梁”组合结构，“悬臂梁+砌体梁”组合结构相互堆砌形成一个支撑上方岩层重力的“拱式”结构。

（3）上分层遗留区段煤柱下斜交工作面过煤柱开采过程中，覆岩垮落区域按破断形式和垮落高度划分为内、外场区域，内场中覆岩的垮落形态特征表现为“拱式”结构：随着工作面与遗留煤柱的位置变化呈现出从非对称型“双拱”型到对称型“双拱”型再到“单拱”型的周期性变化；外场覆岩破断结构体现为：随着工作面与遗留煤柱的位置变化呈现出“O-X”结构到“O-X-Y”结构的周期性变化。

（4）当工作面上、下和中部任何一处顶板存在区段煤柱时，煤柱失稳时原煤柱内的支承压力向工作面两侧转移，且区段煤柱上方岩层为首次破断，顶板破断垮落层位较低，垮落顶板堆积量较小，下方工作面支架工作阻力处于30~34 MPa之间；当顶板为采空区时，发生大量垮落顶板堆积充填现象，造成下方工作面支架工作阻力较大，处于38~42 MPa之间。现场工作面液压支架工作阻力探测数据验证了遗留区段煤柱对下分层工作面液压支架工作阻力影响情况。

The upper and lower layered working faces of fully-mechanized caving mining in extra-thick coal seams are arranged obliquely,and the lower layered fully-mechanized caving working face passes through the coal pillars left by the upper layer intermittently. The fracture movement of overlying strata and the law of mine pressure are complex,which affects the safe mining of the lower layered working face. Based on the engineering background of 25023 lower fully mechanized caving face in Yanbei Coal Mine of Gansu Huating Coal and Electricity Co.,Ltd.,this paper uses the research methods of numerical calculation,physical similarity simulation,theoretical analysis and field measurement to analyze the stress change of surrounding rock and the deformation and failure law of overlying rock in the lower oblique working face of the upper layer residual coal pillar. The variation law of the bearing pressure of the section coal pillar and the lower layer working face during the mining of the upper layer residual coal pillar is obtained,and the evolution characteristics of the overlying rock structure of the fully mechanized caving face passing through the residual coal pillar are revealed. The main conclusions are as follows：

(1) In the numerical calculation experiment,the maximum stress peaks of the two section coal pillars left after the completion of the mining of the three working faces in the upper layer are 42.53 MPa and 41.12 MPa,and the stress concentration factors are 3.24 and 3.35. In the process of coal pillar mining,the lower oblique working face of coal pillar in the upper layered left section periodically enters and leaves the coal pillar. When the coal pillar enters,the lower port transportation roadway first enters the coal pillar,and when the coal pillar leaves,the upper port return airway finally leaves the coal pillar. In the stage of working face entering the remaining section coal pillar,when the working face is 45 m away from the coal pillar,the peak pressure at the transportation roadway reaches 45.3 MPa,which is 13.7 % higher than that when the lower layer is not mined ; in the section coal pillar stage of the working face,when the working face is 15 m away from the coal pillar,the pressure peak at the return air roadway reaches 46.7 MPa,which is 9.9 % higher than that when the lower layer is not mined.

(2) In the process of coal pillar mining,the section coal pillar instability and the large-scale spatial caving of overlying rock are caused. The masonry structure is formed after the long-distance high rock stratum is broken,and the low rock stratum at close distance undergoes secondary breaking to form the ' cantilever beam + masonry beam ' composite structure. The ' cantilever beam + masonry beam ' composite structure is stacked with each other to form an ' arch ' structure supporting the gravity of the upper rock stratum.

(3) In the process of mining the oblique working face under the coal pillar in the upper layer,the caving area of the overburden rock is divided into the inner and outer field areas according to the fracture form and the caving height. The caving morphology of the overburden rock in the inner field is characterized by the ' arch ' structure : with the change of the position of the working face and the remaining coal pillar,it shows a periodic change from the asymmetric ' double arch ' type to the symmetrical ' double arch ' type and then to the ' single arch ' type. The fracture structure of the overlying strata in the field is reflected as follows : with the change of the position of the working face and the remaining coal pillars,the periodic change from the ' O-X ' structure to the ' O-X-Y ' structure is presented.

(4) When there is a section coal pillar in any roof of the upper,lower and middle parts of the working face,the abutment pressure in the original coal pillar is transferred to both sides of the working face when the coal pillar is unstable,and the rock stratum above the section coal pillar is broken for the first time. The caving layer of the roof is low,the accumulation of the caving roof is small,and the working resistance of the support in the lower working face is between 30 MPa and 34 MPa. On the contrary,when the roof is goaf,a large number of collapsed roof accumulation filling occurs,resulting in a large working resistance of the support in the lower working face,which is between 38 MPa and 42 MPa. The detection data of the working resistance of the hydraulic support in the field working face verified the influence of the remaining section coal pillar on the working resistance of the hydraulic support in the lower stratified working face.

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