浅埋非充分垮落区下开采覆岩结构联动失稳机理

Partial caved goaf (PCG) is widely distributed in the western mining area of China. Mining under the PCG will induce instability of overlying strata and cause strong disasters pressure. This project is based on the research background of coal seams mining under shallow buried PCG, the three-dimensional reconstruction and inversion simulation method is used to study the roof collapse characteristics of the PCG, the creep damage characteristics of the residual coal pillar and the distribution law of overburden load on it. The non-linear elastic foundation beam model of the main roof is established, the deformation characteristics of the main roof are analyzed, and combining compaction experiment to determine the bearing characteristics of caved waster in the PCG. The two-dimensional model of the coal-column cellular automata is established to study the influence of the strain energy increment of the cell under the mining action on the stability of the coal pillar, and the internal relationship between the instability mode of the pillar and the evolution of the mining stress is established. Constructing the model for analyzing kinematics of the roof Ⅰ, pillar, Caved waster and Roof Ⅱ, based on the law of the parallel movement and fixed-axis rotation, the relationship between the instability time series of roofs and its induced dynamic load strength is studied by the method of momentum and energy conservation, and the quantitative calculation method of dynamic load is put forward to reveal the mechanism of strong mine pressure disaster caused by the linkage instability of the overlying strata structure in lower coal seam mining. Research results can provide important theoretical support for safe mining of coal seams under the PCG.

我国西部矿区存在大范围非充分垮落采空区，空区下开采易活化覆岩结构联动失稳诱发强矿压致灾。本项目以非充分垮落区下煤层开采为研究背景，采用三维重构与反演的模拟方法，研究采空区顶板垮落特征、残留煤柱蠕变损伤特征及煤柱上覆载荷分布规律，建立基本顶的非线性弹性地基梁模型，解析基本顶变形特征，结合碎石压实试验确定采空区碎石承载特征。基于元胞自动机理论建立煤柱内能量演化模型，研究采动作用下元胞应变能增量对煤柱稳定性的影响，阐释煤柱失稳模式与采动应力演化之间的内在联系。构建“顶板Ⅰ-‘煤柱+碎石’-顶板Ⅱ”结构运动分析力学模型，基于平行移动和定轴转动理论，采用动量、能量守恒方法研究双层顶板失稳时序与其诱发动载强度之间的关系，并提出动载定量计算方法，从而揭示下煤层开采覆岩结构联动失稳诱发强矿压致灾机理。研究成果为非充分垮落区下煤层安全开采提供重要理论支撑。

项目以浅部非充分垮落区下煤层覆岩破断机理与致灾机制为研究对象，综合运用理论计算、物理模拟、数值计算及现场实测等研究手段，明晰了非充分垮落采内顶板稳定特征，阐明了“煤柱-碎石”的协同承载特性及煤柱损伤特征，揭示了采动作用下上覆煤柱与顶板力学行为与响应机理，取得了以下研究成果：（1）提出了3种采空区垮落类型的判别方法，并给出了非充分垮落采空区的定义，且揭示了空区内协同承载单元的承载特性。建立了空区碎石的三维离散元模型，通过加载实验揭示了其承载变形特性；结合间隔式采空区基本顶变形特征，采用分段函数的形式描述了采空区内破碎岩体承载特征。重构了间隔式开采地质模型，研究并揭示了煤柱长期稳定特征与上覆载荷分布规律，空区碎石承载宽度约为20 m，最大支承载荷为1.055 MPa；煤柱单侧塑性区宽度为1.48 m，弹性区支承载荷约为11.33 MPa。（2）基于重整化群理论将间隔式采空区中煤柱群划分为一维重整化煤柱群模型，将煤柱失稳概率密度函数表示为威布尔函数分布形式，计算得出重整化煤柱群元胞失稳概率，利用不动点理论确定元胞失稳不动点方程及其有效解，此解作为判断煤柱失稳概率的临界值。以南梁煤矿为例，计算了间隔式采空区中一维重整化煤柱群中元胞失稳概率，对比煤柱失稳临界值，得出采空区中煤柱群无整体失稳可能性。（3）针对浅埋采场岩层破断易形成大块度关键块的特点，分析两关键块体正向回转与反向回转所形成的动态结构，并建立了关键块相对回转动态力学模型。研究回转过程中结构的力学行为，并进行稳定性分析，找到了回转过程中结构最易失稳点，以支架工作阻力为响应特征，提出了工作阻力确定方法。获得了采动过程中煤柱、上覆岩层破断特征及支架支承压力变化规律，采空区上覆岩层整体呈切断式垮落，其中向沟开采阶段支架工作阻力逐渐降低；空区下开采支架支承压力曲线呈拱形分布且大小较煤柱下偏大约2 MPa，存在煤柱突变失稳、覆岩破断产生冲击载荷致灾的危险。