巨厚煤层重复采动覆岩结构演变及其控制机理研究

The mechanism of overlying strata structure evolution is one of the key basis for the stope surrounding rock control design, when mining the extra-thick coal seam in the condition of large-size mined space and repeatedly disturbance. Based on the typical geological condition of flat extra-thick coal seam of Xinjiang Uighur Autonomous Region, aiming at the differences of composition structure of overlying strata and the changes of mined space, this project takes overlying strata structure of longwall mining stope as an object, systematically analyze the law of the overlying strata breakage and movement during mining by using simulated experiment method, focus on the mechanical transmission and the hinged characteristics of breakage and unloaded overlying strata during repeated mining. This project reveals dynamic evolution of the mining overlying strata, determines the overlying strata structure variation characteristics of spatial form and evolution features of boundary restriction related by the mined space expanding and time increasing. The control mechanism of overlying strata structure stability will be determined by analyzing instability characteristics, occurred conditions and key influential factors. Combine the characteristics of mining-induced stress change and fractures extension, the whole mechanical model of strata structure will be established, which is named "wall-support-overlying strata", and analyze load forms, variation characteristics of overlying strata and reciprocity relationship of the "support - surrounding rock" , determine the calculation method of the working resistance of hydraulic support in longwall face, propose basic strategy and effective method which used to control overlying strata, thereby, these scientific and technical achievements will provide theoretical references for improving roof control technologies, optimizing mine development and deployment of extra-thick coal mining in this area.

大尺度开采空间与多频次开采扰动下覆岩结构的演变规律是巨厚煤层重复开采采场围岩控制设计的关键基础之一。基于新疆典型近水平巨厚煤层地质条件，以长壁采场覆岩结构为研究对象，针对覆岩组成结构的差异与开采空间的变化，采用物理模拟和数值计算的方法，系统分析开采过程中覆岩的破断运动规律，重点研究重复采动时卸荷破断岩块间的力学传递与铰接特征，揭示采动覆岩结构的动态演变过程，掌握随开采空间扩展与采动次数增加覆岩结构空间形态的变化特征和边界约束条件的演化特点，通过系统分析采动覆岩结构的失稳特征、产生条件及关键影响因素，明确采动覆岩稳定性控制机理；结合采动应力变化与裂隙扩展特征，建立"煤壁-支架-覆岩"整体结构力学模型，分析覆岩的载荷形式与变化特征及"支架-围岩"相互作用关系，寻求工作面支架阻力计算方法，提出控制采动覆岩失稳的基本对策与有效方法，为巨厚煤层开采顶板控制技术完善、矿井开拓部署优化等提供理论借鉴。

新疆作为我国第十四个亿吨级煤炭基地，是重要的能源接替区和战略能源储备区，区内广泛赋存有巨厚煤层。本项目针对目前开发较为集中的准东煤田典型巨厚煤层赋存条件，综合运用现场调研、理论分析、实验测试、物理模拟和数值计算等方法，围绕大尺度开采空间扩展与多频次应力扰动条件下覆岩结构演变特征及其稳定性控制开展了系统研究。取得的主要成果有：.①明确了初次采动空间变化对岩层破断运动特征的影响。基于典型巨厚煤层代表性煤岩样力学参数，对比分析了养护湿度、时间对相似材料强度的影响，掌握了首采分层一次采出厚度变化对采动应力分布和采动裂隙扩展的影响，即随首分层采厚增大，顶板裂隙更为发育，覆岩承载结构上移，来压强度增大。.②掌握了巨厚煤层重复采动时顶板及覆岩结构的演变过程和形态变化的临界条件。引入电法测试方法，明确了覆岩裂隙发育程度和岩层电位呈正相关变化关系；覆岩发生二次破断、顶板铰接结构弱化并呈现“梁式结构—高位梁式结构—拱式结构”结构演变过程，认为分层采厚是覆岩结构失稳的关键影响因素，随着分层采厚增大，覆岩结构稳定性降低，提出了以深厚比为主要指标的覆岩结构形态判别方法。.③研究了巨厚煤层多分层开采各阶段支架需控围岩的变化特征及“支架—围岩”关系。建立了“煤壁—支架—覆岩”整体结构力学模型，揭示了支架需控围岩“由梁式结构的基本顶及其下方岩层到拱式结构的拱内松散岩块”的变化特征，明确了支架载荷主要来源，提出了相应的支架工作阻力计算方法。.④确定了巨厚煤层“先厚后薄、减少分层”的开采原则，提出了以顶煤冒放性、煤壁稳定性、底煤破坏深度等为约束条件的分层采厚划分方法和以煤层倾角、开采总厚、覆岩厚度为评价指标的开采工艺选择原则。探索了“利用煤体碎胀支撑顶板减小采动影响、合理划分分层采厚利用采动影响多次碎矸提高顶煤放出效果、折返式立体化巷道布置提升开采效率、大范围梯度开采控制地表台阶下沉”等实现巨厚煤层安全高效绿色开采的对策方法。