高、低阶纵波组合模式下复合结构煤岩体动态损伤机理

Coal and rock masses in deep mining would bear dynamic disturbances and it is the excitation power of coal and gas outburst, which propagates deep into the coal rock mass in the form of stress wave. These stress waves were mainly composed of high order P-waves with high frequency, fast phase velocity and many wave numbers. Because of absorption and dispersion effect in propagation of waves, the high order P-waves would change into low order P-waves with low frequency, slow phase velocity and less wave numbers. In the process of coal and gas outburst, the expansion of crack and failure of structural surface would also produce a large number of high and low order P-waves. Therefore, in the dynamic process of excitation, formation, development and termination of coal and gas outburst, there are always high and low order P-waves propagating in coal and rock masses. Moreover, the propagation velocity of P-waves was fast and firstly acted on coal and rock masses, which played the very important role in its dynamic damage. The areas of coal and gas outburst were composed of coal-rock masses with composite structure, so reflection, transmission and diffraction phenomena would happen at the interface in the propagation of high and low order P-waves, resulting in dynamic effect, such as reflected tension, convergence, superposition and stress mutation in reflection /transmission, which caused the dynamic damage and occurrence of coal and gas outburst. Taking the coal rock massed with composite structure as the research object, the propagation and action mechanism of high and low order P-waves would be researched to establish the dynamic distribution models of displacement, stress, and energy transmission. The dynamic distribution of displacement field, stress field and energy field would be obtained to reveal the dynamic damage mechanism of coal and rock masses with composite structure, which provided theoretical support for improving the mechanism of coal and gas outburst and other dynamic disasters.

深部煤岩体掘进时承载的动力扰动是煤与瓦斯突出的激发动力，它以应力波的形式向煤岩体深部传播；此应力波主要由频次高、相速度快、波数多的高阶纵波组成，在传播中由于吸收、弥散效应会转变成频次低、相速度慢、波数少的低阶纵波；而且突出中煤岩体内部裂纹萌生、扩展也会产生大量的高、低阶纵波，因此，在突出的激发、形成、发展与终止的整个过程，煤岩体中始终存在着高、低阶纵波的传播与作用。同时，由于突出区域是由复合煤岩体构成的，纵波传播时会在分界面发生明显的反射、透射等现象，致使反射拉伸、汇聚叠加、反/透射应力突变等动态效应的产生，易导致煤岩体发生动态损伤与破坏，为突出奠定基础。以整体复合结构煤岩体为研究对象，研究高、低阶纵波在煤岩体中的传播与作用机制，建立位移、应力与能量传播与动态分布计算模型，得出煤岩体中位移场、应力场、能量场“三场”动态分布规律，揭示复合结构煤岩体的动态损伤机理，为完善突出机理提供理论支撑。

煤与瓦斯突出的发生是在外部扰动条件下，由多层复合煤岩体共同作用的结果，其动态响应特征与损伤模式亟待研究。基于SHPB冲击实验研究了高速冲击作用下不同组合顺序的复合煤岩体的动态响应特征，有围压或无围压多层复合煤岩体的应力、应变的时程变化曲线、应力-应变动态变化曲线均可分为五个阶段；发生损伤前，多层组合煤岩体的力学性质在冲击方向上具有趋同性。基于应力波传播理论，分析了复合煤岩体中应力波的传播与作用机制，得出拉应力产生区域集中分布在力学性质差异较大的煤岩体中，与卸载波的作用紧密相关，是导致层裂现象产生的关键因素。推导了柱面波传播的频率方程，建立了高、低阶纵波模式下圆柱形煤岩体中位移、应力、应变与振速动态计算模型，得出圆心处的位移、应变、应力、振速及能量动态变化幅值最大。建立了薄板煤岩体自由振动的Hamilton体系对偶方程、挠度动态分布方程，分析了应力、应变、能量的分布规律，得出薄板岩体的振型主要由1阶、5阶、6阶主振型叠加构成。基于相似材料实验结果可知复合煤岩体界面振动的振幅呈现出先增加再衰减两个阶段，其动态衰减符合指数变化的规律；得出了界面振动振幅-频率的频谱结构，其两个卓越频率分别为48.9Hz~53.7Hz、92.4Hz；基于希尔伯特-黄变换，可知IMF1、IMF2、IMF3的能量较高，为有效振型；IMF2能量占比最高，其卓越频率集中在45.6Hz~50.2HZ，在振动过程中起决定作用，实际生产中可根据煤岩体的尺寸与力学性质进行换算得到实际卓越频率。结合实验与数值模拟结果得出了薄板岩体的1阶振型的振幅最大，决定薄板岩体的初始损伤位置；高阶纵波模式下煤岩体在无围压条件下易发生脆性劈裂破坏，低阶纵波模式下煤岩体以剪切破坏为主；无围压多层复合煤岩体的动态破坏模式主要以拉-剪破坏为主，其中力学强度相对较低的“弱层”是初期承载的主体，会首先发生损伤甚至破坏。项目研究初步揭示了高、低阶纵波组合模式下复合结构煤岩体的动态损伤机理，对揭示煤与瓦斯突出等动力灾害的发生机理具有重要意义。