分阶段卸载条件下突出煤变形特征与渗流特性

为研究下保护层开采过程中采动应力作用下含瓦斯突出煤的渗流特性,利用自制的三轴渗流试验机,进行了恒定轴压卸围压、增大轴压卸围压、轴压围压同时卸载等3种不同加卸载条件下的分阶段卸围压煤样瓦斯渗流试验。试验结果表明:试验中煤样的变形具有明显的阶梯状特性,煤样未破坏时,应变增量随着围压卸载速率的增大而增大。随着围压的卸载,恒定轴压卸围压组和增大轴压卸围压组煤样的偏应力不断增大,其渗透率则呈现出先减小后增大的趋势,而轴压和围压同时卸载组煤样的渗透率则随着围压的卸载,呈现出不断增大的趋势。煤样体积应变变化量较大时,渗透率变化量也大。从能量的角度分析渗透率的变化,发现煤样渗透率均随能量耗散率的增大而呈指数增大。

Deformation and permeability characteristic of outburst coal under step unloading conditions

To analyze the permeability law of outburst coal under mining stress field during lower protective seam mining，the gas permeation experiment of coal samples was carried out by the triaxial gas-seepage test machine under the process of different ways (constant axial pressure，loading axial pressure，and unloading axial pressure) of step unloading confining pressure with different rates.The results show that：The deformation of coal samples has obvious ladder shape characteristics in the experiment.When the coal samples are not destroyed，the strain increment of the coal samples increases with the increase of the unloading rate of confining pressure.As the unloading of confining pressure，the deviator stress of coal samples under the unloading confining pressure with constant axial pressure and unloading confining pressure with loading axial pressure increase，and its permeability shows a trend of decrease initially and then increase.The permeability of coal samples under unloading axial pressure and confining pressure at the same time increases with the unloading of confining pressure.When the change of the volume strain of coal samples is large，the variation of permeability is large.Analysis on the change of permeability of coal samples is based on the energy，and the permeability of coal samples increases exponentially with the increase of the energy dissipation rate.