离层储水动压带结构演化及失稳冲击致灾机理

Structural evolution and instability induced shock disaster mechanism of bed separation water bearing dynamic pressure zone

  • 摘要: 离层动压突水具有瞬时量大、破坏性强和突水征兆不明显等特点,致灾风险极高,防控难度极大。为了探究离层动压突水的孕灾过程和冲击致灾机理,本研究针对覆岩赋存充水含水层的煤层采动过程,提出了覆岩离层储水动压带的纵向分区概念。分区域阐明了离层储水动压带的形成机制,系统性地提出上位动压储能、中位离层储水和下位侵蚀隔水等决定性因素是离层动压突水的主要孕灾条件。引入阶梯状组合梁接触载荷模型,优化覆岩动态离层层位分析方法,计算了煤层开采过程中覆岩离层空间的动态发育层位。基于爆破动载致裂理论,构建了动压传递等效水不耦合爆炸模型,将岩层破断能量转化为上位动压储能区等效动载,运用冲击波衰减理论,求解了中位离层储水区冲击压力,引入动态增强因子,建立动态强度与下位侵蚀隔水区岩体应力的关系方程,推导了离层动压突水动力破坏半径的计算公式,提出了离层储水动压带失稳冲击致灾机理。以红柳煤矿1121工作面为例,采用井下仰孔分段注水方法实测了导水裂隙带发育高度约为36 m,理论分析了覆岩离层空间的动态发育过程,计算了离层储水动压带失稳冲击致灾半径,建立了离层储水动压带失稳冲击致灾判据。判定结果表明:1121工作面离层储水动压带失稳会冲破下位侵蚀隔水区岩层,导致大型透水事故发生。现场覆岩结构探测结果证实了粗砂岩上分层破断是第4次透水发生的主要动力源。实验室利用水化学分析测试确定了粗砂岩含水层为第4次透水的主要充水水源,验证了离层储水动压带失稳冲击致灾机理的正确性,研究成果为类似条件的采动覆岩离层动压突水灾害防治提供了理论借鉴。

     

    Abstract: Bed separation dynamic pressure water inrush is characterized by large instantaneous water inflow, strong destructiveness, and inconspicuous pre inrush signs, resulting in extremely high disaster risk and great difficulty in prevention and control. To investigate its disaster forming process and shock induced disaster mechanism, this study proposes the concept of longitudinal zoning of the overburden bed separation water bearing dynamic pressure zone (BSWBDPZ) for coal mining under overburden strata containing water filled aquifers. The formation mechanism of the BSWBDPZ is clarified for each zone, and upper dynamic pressure energy storage, middle bed separation water storage, and the lower eroded aquiclude zone are systematically identified as the decisive factors and main disaster forming conditions for bed separation dynamic pressure water inrush. A stepped composite beam contact load model is introduced to optimize the method for analyzing dynamic bed separation horizons in overburden strata, and the dynamic development horizons of overburden bed separation spaces during coal mining are calculated. Based on the theory of dynamic load induced cracking under blasting, an equivalent water decoupled blasting model for dynamic pressure transmission is constructed. The breaking energy of rock strata is converted into an equivalent dynamic load in the upper dynamic pressure energy storage zone, and the shock pressure in the middle bed separation water storage zone is solved using shock wave attenuation theory. By introducing a dynamic enhancement factor, a relational equation between dynamic strength and rock mass stress in the lower eroded aquiclude zone is established. A formula for calculating the dynamic failure radius of bed separation dynamic pressure water inrush is derived, and the shock induced disaster mechanism caused by instability of the BSWBDPZ is proposed. Taking 1121 working face of Hongliu Coal Mine as an example, the development height of the water conducting fractured zone was measured to be approximately 36 m using the underground upward borehole sectional water injection method. The dynamic development process of overburden bed separation spaces was theoretically analyzed, the shock induced disaster radius caused by instability of the BSWBDPZ was calculated, and corresponding instability induced disaster criteria were established. The evaluation results show that instability of the BSWBDPZ in 1121 working face would break through the rock strata of the lower eroded aquiclude zone, resulting in a major water inrush accident. Field detection of the overburden structure confirmed that fracturing of the upper sublayer of the coarse sandstone was the main dynamic source of the fourth water inrush. Laboratory hydrochemical analysis identified the aquifer above the coarse sandstone as the main water source of the fourth water inrush, thereby verifying the validity of the shock induced disaster mechanism caused by instability of the BSWBDPZ. The research findings provide a theoretical reference for the prevention and control of bed separation dynamic pressure water inrush disasters in mining induced overburden strata under similar conditions.

     

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