煤矿冲击地压与断层构造失稳的多物理场互馈机制研究进展

A review on the interaction mechanism between coal bursts and fault structure instability from the perspective of multi physical field

  • 摘要: 煤矿冲击地压与断层构造失稳的多物理场互馈机制研究对于保障煤炭资源安全高效开采具有重要的科学意义和工程指导价值。人类采掘活动使得在地壳运动等强挤压过程中形成的断层等复杂地质构造受到扰动,结构面的活化和失稳将释放大量在构造成型期间所积聚的弹性应变能,进而极易诱发冲击地压等动力灾害。从断层构造成因、地质赋存状态和高水平原岩应力环境的角度介绍了冲击地压发生的地质环境特征,总结了与断层构造相关的冲击地压发生模式,凝练了开采扰动下断层滑移失稳的力学机理和断层构造失稳诱冲的多物理场前兆特征等2个关键科学问题,建立了考虑工作面开采影响的断层结构力学模型和厚层顶板赋存的物理模型,推导了断层面上下盘相对滑动位移计算的逐点积分方法,提出了可表征断层滑动摩擦与能量释放相关性的断层结构势能的概念,分析了开采扰动下断层面位移场、应力场和能量场的动态演化特征,系统阐述了断层构造的失稳特点和诱冲力学机理。研究结果显示,工作面开采条件下断层区域位移场表现为由局部静态滑移突然向整体剧烈滑动转变的非线性动态演化过程,并伴随着断层面上下盘之间的相对位移出现由缓慢滑动突然变化为急剧滑移的失稳现象,断层面最大位移也由断层顶部突然转移至断层中部靠近煤层的区域,对工作面造成极大冲击破坏。随着煤层的逐步开采,断层面正应力和剪应力在同步演化发展过程中发生了分化的现象,表现出正应力增加而剪应力降低或剪应力增加而正应力降低的特征。断层结构面和上覆厚层顶板的交界区域在上覆岩层下沉和侧向压力的共同作用下完成了最大滑动静摩擦向滑动失稳摩擦的动态转换过程,位移场的缓急突变和应力场的正剪分化现象均出现在该转换期间,而最大位移的出现也预示着断层结构发生了剧烈的滑移失稳。断层结构失稳前,由于厚层顶板坚硬且不易破断使得断层结构保持相对稳定,此时断层结构势能处于长期积聚而未释放的状态。监测数据显示,与断层结构势能相关的微震事件数、声发射事件数和电磁辐射强度值等数据均出现缺失的现象。断层滑移失稳后,该类监测数据又由几乎为零转为突然激增,并伴随着剧烈的滑动和对工作面的冲击破坏。综上所述,在复杂断层构造赋存、高水平原岩应力环境和开采扰动下,岩层运动与断层滑移的耦合作用是断层失稳的主要原因,而伴随的位移场缓急突变、应力场正剪分化和能量场激增滞后等多物理场演化规律均可作为冲击地压发生的前兆特征。

     

    Abstract: The study on the interaction mechanism between coal bursts and fault structure instability from the perspective of multi physical field has great scientific significance and practical value for ensuring safe and efficient mining of coal resources. Human excavation activities can disturb fault structures formed by intense compression such as crustal movement. A large amount of elastic strain energy accumulated during the fault formation will be released due to the reactivation and instability of fault structure, which is bound to induce dynamic disasters such as coal bursts. The geological occurrence environment of fault structure when a coal burst happens is introduced from the point of view of reasons and the state of fault structure formation, and the high level stress environment. The model of the occurrence of coal burst related to fault structure is summarized. Two key scientific problems are concluded: the mechanical mechanism of fault slip under mining disturbance and the precursor characteristics of multi physical field of coal burst induced by fault instability. A physical model with the existence of fault structure and extra thick rock strata is established with the mining activities considered. A point by point integration calculated methodology of fault relative slip is deduced. The concept of fault structure potential energy characterizing the correlation between the sliding friction of fault and energy release is proposed. The dynamic evolution characteristics of fault structural displacement field, stress field and energy field under mining disturbance are analyzed. The characteristics of fault instability and the mechanical mechanism of fault induced coal burst are systematically explained. The results show that a nonlinear dynamic evolution from local static slip to global violent slip can be observed on fault structure under the mining disturbance. Meanwhile, the relative displacement between the fault hanging wall and footwall changes from slow slip to sudden and sharp slip under the mining disturbance, and the maximum displacement on the fault suddenly moves from the top of fault to the middle near the coal seam, which causes serious damage to mining safety. The evolution of the normal stress and shear stress is from synchronous development to differentiated appearance, that is, the normal stress increases and the shear stress decreases or the shear stress increases and the normal stress decreases. Under the lateral pressure and overburden subsidence pressure, the transformation from maximum sliding static friction to sliding instability friction occurs at the interaction zone between fault structure and overlying extra thick rock. The abrupt change of fault displacement field and the differentiation of stress field both occur during this transformation. The appearance of the maximum displacement on the fault plane indicates the severe slips of fault structure. Before the fault instability occurs, the fault structure remains relatively stable because the overlying extra thick rock near the fault is not easy to be fractured, and the fault structure potential energy is accumulated for a long time but not released. The monitoring data shows that the number of micro seismic events, acoustic emission events and electromagnetic radiation intensity exist the missing phenomenon. The value of fault structure potential energy suddenly increases from almost zero after the fault instability occurs, and the severe fault slips and coal bursts are usually accompanied. In conclusion, the coupling effect of overlying strata movement and fault slip is the main cause of fault slip under the condition of existence of fault structure, the high level stress environment and mining disturbance. The evolution characteristics of multiple physical fields can be used as the precursory characteristics of coal burst, such as the sudden change from a steady state of displacement field, the differentiation between normal and shear stress of stress field, and the sharp increase and hysteresis of energy field.

     

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