动静荷载下含瓦斯煤能量耗散与破碎特征试验研究

Experimental study on energy dissipation and fragmentation characteristics of gas-bearing coal under combined dynamic and static loading

  • 摘要: 为探究动静荷载下含瓦斯煤能量耗散与破碎特征,利用自主研制的可视化含瓦斯煤动静组合加载试验系统,开展了不同冲击速度与轴压比条件下含瓦斯煤冲击试验,探究含瓦斯煤破裂能量演化特征与耗能特性,探讨碎屑弹射机制及其分布特征,以期阐明含瓦斯煤耗能密度与碎屑分形间的内在联系。结果表明:① 含瓦斯煤冲击过程能量转化具有同步性,且耗散能时程曲线与煤体变形阶段相对应,即当含瓦斯煤丧失承载能力时,动态应力−应变曲线形态为抛物线型,耗散能时程曲线划分为弹性储能、弹塑性耗能、塑性耗能与能量释放阶段;特别地,当轴压导致含瓦斯煤处于弹塑性或塑性状态时,耗散能时程曲线可直接划分为弹塑性或塑性耗能阶段与能量释放阶段;当含瓦斯煤仍具有承载能力时,动态应力−应变曲线形态为倒钩型,耗散能时程曲线划分为弹性储能、弹塑性耗能、塑性耗能与耗散能回弹阶段,耗散能回弹阶段可导致煤壁片帮或巷道岩爆。② 含瓦斯煤耗散能随冲击速度升高而增大,耗能占比基本恒定,其值介于31.1%~34.0%,碎屑分维随耗能密度升高呈指数增长;存在临界轴压比使耗散能与耗能占比呈先下降后上升趋势,碎屑分维随耗能密度变化具有分段性,当试样处于持续储能阶段,碎屑分维随耗能密度的增加而降低;当试样处于持续释能阶段,碎屑分维随耗能密度的增加而升高,此时轻微动力扰动即可导致煤岩失稳。研究丰富了煤岩瓦斯动力灾害诱发机制的基础理论,可为煤岩瓦斯动力灾害的监测、预警以及防治技术提供理论支撑。

     

    Abstract: To explore the energy dissipation and fragmentation characteristics of gas-bearing coal under combined dynamic and static load, the impact experiment of gas-bearing coal under different impact velocities and axial compressive stress ratios was carried out with the help of the self-developed observable combined dynamic and static loading test system of gas-bearing coal. The energy evolution laws and energy dissipation characteristics of gas-bearing coal fracture were studied. The debris ejection mechanism and its distribution characteristics were discussed, the intrinsic relationship between the energy dissipation density and the debris fractal dimension of gas-bearing coal was clarified. The results show that: ① The energy conversion of gas-bearing coal during impact is synchronous, and the time curve of dissipation energy corresponds to the deformation stage of coal sample, that is, it is found that when the bearing capacity of gas-bearing coal is lost after impacted, the dynamic stress-strain curve is parabolic, and the time curve of dissipation energy can be divided into elastic-energy storage stage, elastic-plastic-energy dissipation stage, plastic-energy dissipation stage and energy release stage. Especially, when the axial load causes the gas-bearing coal to be in an elastic-plastic or plastic state, the time curve of dissipation energy is divided into the elastic-plastic or plastic energy dissipation stage and the energy release stage. When the gas-bearing coal still has bearing capacity after impacted, the dynamic stress-strain curve is barbed, and the deformation stage can be divided into elastic stage, elastic-plastic stage, plastic stage and rebound stage. the time curve of dissipation energy is correspondingly divided into elastic-energy storage stage, elastic-plastic-energy dissipation stage, plastic-energy dissipation stage and energy-rebound stage. The energy rebound stage can lead to coal wall spalling or roadway rockbursts. ② The dissipation energy of gas-bearing coal increases with the impact velocity increasing, the dissipation energy ratio is basically constant, which is between 31.1%−34.0%. The fractal dimension of debris increases exponentially with the increase of energy dissipation density. There is a critical axial compressive stress ratio, which makes the dissipation energy and its ratio decrease first and then increase. The fractal dimension of debris is segmented with the change of energy dissipation density: when the sample is in the continuous energy-storage stage, the fractal dimension of debris decreases with the increase of energy dissipation density, when the sample is in the continuous energy-release stage, the fractal dimension of debris increases with the energy dissipation density increasing, and at this point, slight disturbances can lead to coal-rock instability. These conclusions enrich the basic theory of the dynamic coal–rock–gas disaster induction mechanism and can provide theoretical support for the monitoring, early warning and prevention technology of dynamic disasters in composites.

     

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