矿震对含气煤样力学及渗流特性影响规律

Influence of mine earthquake on mechanics and seepage characteristics of gas-bearing coal

  • 摘要: 矿震频发给煤矿安全生产带来严重威胁,经调研表明矿震后易引发瓦斯灾害,呈现“先震后灾”特征,为矿震作用下瓦斯灾害预警提供了可能,但矿震作用诱发瓦斯灾害渗流规律不清。考虑煤体应力环境及瓦斯灾害发生原理,基于矿震波形特征分析,采用自主设计的动态三轴加载渗流试验系统,引入循环应力比(Cyclic Stress Ratio, CSR)来模拟矿震作用特征,同时考虑了动载频率和气体吸附压力,设计了动静组合加载方式,研究了动载作用下含气煤样的力学、微观孔隙及渗流特性。结果表明:在动载加载阶段煤样残余应变随振动次数开始快速增大后逐渐趋于平缓,煤样渗透率随动载频率和CSR的增大呈指数函数增大,而与初始吸附气体压力呈负指数函数变化,且CSR对煤样力学和渗透率影响最显著;损伤后的含气煤样峰值强度和弹性模量与动载频率、CSR、气体吸附压力均呈负相关关系,在CSR为0.75时峰值强度和弹性模量劣化率达到最大,分别为15.3%和68.2%,损伤变量为0.68;利用CT扫描和三维重构技术,得到煤样加载前后孔隙体积变化的定量表征,不同CSR加载下孔隙总体积最大增大到初始状态的7倍,分析了动荷载对煤样孔隙率的影响特征,解释了矿震动应力对煤体孔裂隙发展、渗流特征及损伤变形的作用特征及相关关系。研究可为矿震作用下深部煤岩瓦斯动力灾害的机理揭示及灾害预警提供支撑。

     

    Abstract: Frequent occurrence of mine earthquakes poses a serious threat to coal mine safety production. According to the investigation, it is easy to cause gas disasters after the mine earthquake, showing the characteristics of “earthquake first and disaster later”, which provides the possibility of early warning of gas disasters under the action of mine earthquake. However, the seepage law of gas disasters induced by mine earthquake is not clear. Considering the stress environment of coal body and the occurrence principle of gas disaster, based on the analysis of mine earthquake waveform characteristics, a self-designed dynamic triaxial loading seepage test system was adopted, and cyclic stress ratio (CSR) was introduced to simulate the characteristics of mine earthquake. At the same time, the dynamic load frequency and gas adsorption pressure were considered. The dynamic and static combined loading scheme was designed, and the mechanical, microscopic pore and seepage characteristics of gas-bearing coal samples under dynamic load were studied. The results show that the residual strain of coal samples increases rapidly with the increase of vibration times at the beginning of dynamic load loading stage, and then gradually tends to be gentle. The permeability of coal samples increases exponentially with the increase of dynamic load frequency and CSR, while it changes in a negative exponential function with the initial adsorption gas pressure, and CSR has the most significant effect on the mechanics and permeability of coal samples. The peak strength and elastic modulus of gas-bearing coal samples after damage are negatively correlated with dynamic load frequency, CSR and gas adsorption pressure. When CSR is 0.75, peak strength and elastic modulus degradation rate reach the maximum, which are 15.3% and 68.2% respectively, and the damage variable is 0.68. Using CT scanning and three-dimensional reconstruction technology, the quantitative characterization of pore volume changes before and after loading of coal samples was obtained. The total pore volume increased to 7 times of the initial state under different CSR loading. The influence characteristics of dynamic load on the porosity of coal samples were analyzed, and the effects of mine vibration stress on the development of pore cracks, seepage characteristics and damage deformation of coal were explained. The research can provide support for the mechanism revelation and disaster warning of deep coal-rock gas dynamic disasters under the action of mine earthquake.

     

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