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乌达矿区浅埋多煤层采动裂隙演化及地表沉降特征

Study on the evolution of mining—induced fractures and surface subsidence characteristics in challow—buried multi—sea m conditions: a case study of wuda mining area

  • 摘要: 针对多煤层重复采动条件下覆岩裂隙发育复杂、地表多次扰动等难题,以浅埋多煤层工作面为研究对象,基于DEM数值模拟结果,引入分形几何理论对重复采动覆岩裂隙进行量化表征,并结合裂隙率理论计算,阐明了煤层群采动裂隙演化及地表损伤规律。研究表明:①随着煤层下行开采,裂隙经历“激活—扩张—压实—再激活”的周期性演化过程,近距离开采下,覆岩破断角保持相同趋势,随着煤层间距增大扰动效应减弱,形成不同的覆岩破断角,裂隙形态呈“双梯形”。②基于分形几何理论揭示了煤层群采动裂隙多次扰动、分区演化的复杂发育特征,通过整体分形得知首层煤开采后分形结果在不同因素影响下稳定增长,平均增量维持在0.06左右,而下伏煤层开采后受扰动影响呈先减小闭合后增大扩张的趋势,相较于近距离开采,较大层间距下的整体分形结果受扰动影响更为显著;分区分形维数表征了不同区域采动裂隙的发育程度,并将其分为“裂隙发育区—扰动激活区—闭合压实区”。③利用图像处理技术提取裂隙长度得出,埋深小于100 m的区域裂隙平均长度为39.4 m,远高于埋深在100 m以下的23.7 m;通过对不同位置裂隙率以及其增量进行计算分析,在间距21.26 m至27.42 m时上层扰动裂隙率增量显著,在间距为86.8 m时扰动效应衰减,裂隙率增量较少,地表下沉量增加,裂隙随采动呈现扩展与闭合交替的动态演化特征。④根据模拟结果、地表最大下沉模型和概率积分法对地表沉陷进行预计,结果绝对误差不超过3.6%;由地表沉降与裂隙演化关系曲线得出浅埋多煤层采动下地表沉降量与裂隙发育呈正相关。研究结果可为浅埋多煤层矿区采动裂隙分析与沉降预测提供理论支撑与方法参考。

     

    Abstract: Ai ming at the co mplex fracture develop ment in overburden and repeated surface disturbance under multi-sea m repeated mining, focuses on shallow-buried multi-sea m working faces. Based on DEM si mulation, fractal geo metry is e mployed to quantitatively characterize overburden fractures, and fracture rate theory is introduced to clarify the evolution of fracture develop ment and surface da mage in coal sea m groups. The results show: ① As mining progresses downward, fractures undergo a cyclic evolution process of “activation–expansion–co mpaction–reactivation.” Under close-distance mining, the overburden breakage angle maintains a consistent trend, while the disturbance effect weakens with increasing sea m spacing, leading to divergent breakage angles and a “double-trapezoid” fracture morphology. ② Fractal geo metry theory reveals the multi-disturbance and zonal evolution characteristics of fractures in multi-sea m mining. Global fractal analysis indicates that after the first sea m extraction, the fractal di mension exhibits steady growth (average incre ment: 0.06) under various factors, whereas subsequent extractions cause an initial decrease (fracture closure) followed by expansion. Notably, larger sea m spacings exhibit stronger disturbance effects on fractal di mensions co mpared to close-distance mining. Zonal fractal di mensions further classify fracture develop ment into three regions: “fracture—developed zone,” “disturbance-activated zone,” and “co mpaction-closed zone.” ③ I mage processing techniques were e mployed to extract fracture lengths, showing an average length of 39.4 m for fractures at depths <100 m, significantly higher than those below 100 m (23.7 m). Fracture rate analysis de monstrates pronounced incre mental growth (21.26–27.42 m sea m spacing) but attenuated disturbance effects at 86.8 m spacing, coinciding with increased surface subsidence. Fractures dyna mically alternate between propagation and closure during mining. ④ Surface subsidence predictions, integrating si mulation results, maxi mu m subsidence models, and the probability integral method, achieved absolute errors ≤3.6%. A positive correlation was identified between surface subsidence and fracture develop ment in shallow multi-sea m mining.

     

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