弱胶结含砾岩层覆岩断裂及应力变化特征研究

    Study on fracture and stress variation characteristics of overlying rock with weakly consolidated gravel layer

    • 摘要: 蒙西地区广泛分布着弱胶结软岩地层,当上覆厚砾岩层时,对覆岩断裂及应力分布影响显著,掌握弱胶结含砾岩层覆岩断裂及应力分布特征对蒙西地区覆岩稳定性评估及卸压范围研究具有重要的指导意义。以红庆梁煤矿为研究背景,采用理论分析、室内试验、数值模拟、现场监测相结合的研究方法,结合3-1煤上覆岩层岩性及分布特征,探讨弱胶结含砾岩层覆岩断裂过程及形式,分析覆岩裂隙发育和应力变化规律,并采用微震监测进行工程验证。研究结果表明:弱胶结含砾岩层覆岩断裂过程分为垮落带垮落、砾岩分层断裂、覆岩整体断裂、覆岩弯曲下沉4个阶段,砾岩层呈“缓慢增加−迅速增大−急剧减小−趋于平稳”的应变变化特征,经历“分层断裂−回转−挤压呈铰接结构岩块”的破坏过程;砾岩层在覆岩破断运移中起到主控作用,上覆岩层随之协调弯曲下沉,破坏程度较低且整体连续性较好;砾岩层多发生张拉破坏裂隙,砾岩层断裂后覆岩裂隙和卸压范围在垂直方向上趋于稳定,裂隙发育高度约52.8 m,通过覆岩应力集中系数分布特征得到卸压范围约79 m。微震监测期间,砾岩层断裂程度较大,单次释放能量较高,最大释放能量8 723.36 J,共发生249次;上部岩层破裂程度较低但密集,微震事件发生频次较多,共发生658次,最大释放能量7 432.52 J。

       

      Abstract: The western Inner Mongolia region is characterized by widespread weakly cemented soft rock strata, where the presence of thick overlying gravel layers exerts a significant influence on roof failure and stress distribution. Understanding the fracture behavior and stress distribution characteristics of weakly cemented gravel-bearing layers is critical for assessing roof stability and determining the extent of pressure release zones in this region. Using Hongqingliang Coal Mine as a case study, this research integrates theoretical analysis, laboratory experiments, numerical simulations, and field monitoring, focuses on the lithological and spatial distribution features of 3-1 coal overburden, and the study investigates the fracture mechanisms and modes of the overlying roof in weakly cemented gravel-bearing strata. The evolution of roof fractures and associated stress variations are analyzed with engineering validation through micro-seismic monitoring. The findings reveal that the roof fracture process in weakly cemented gravel-bearing strata occurs in four distinct stages: caving zone subsidence, stratified fracture of the gravel, overall roof failure, and roof bending-sagging. The strain response in the gravel layer follows a distinct “slow increase - rapid increase - sharp decrease-stabilization” pattern, with failure progressing of “stratified fracture, rotation, and compression into hinged rock blocks”. The gravel layer plays a pivotal role in controlling roof failure, with the overlying strata bending and sinking in a coordinated manner, exhibiting relatively low damage and maintaining overall continuity. Tensile failure is predominant in the gravel layer, and after fracture, roof fissures and the pressure release zone stabilize vertically, with the fissure development height reaching approximately 52.8 meters. The pressure release zone extends to about 79 meters, as indicated by the distribution of roof stress concentration factors. During the micro-seismic monitoring period, the fracture degree of the gravel layer was large, and the single energy release was high, with a maximum of 8 723.36 J, which occurred 249 times; the upper rock layer was relatively low but dense, and the microseismic events occurred more frequently, with a total of 658 times, and the maximum energy release was 7 432.52 J.

       

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