垮落带破碎煤岩样循环加卸载渗流特征实验研究

Experimental study on seepage characteristics of broken coal and rock samples in caving zone under cyclic loading and unloading

在煤层群开采过程中,前期开采煤层形成的采空区垮落带将会受到后期开采煤层的重复扰动,垮落带内的破碎煤岩体将会进一步破碎,进而影响瓦斯在采空区中的运移情况。本文简要总结了国内外针对采空区垮落带内应力、孔隙率、渗透率等参数随着工作面推进的变化关系的研究成果,给出了采空区压实过程中应力及渗透率的预测方法,并在此基础上进行了不同煤岩比例的破碎煤岩样重复加卸载的渗流实验。实验结果表明:颗粒的再次破碎及结构调整,是破碎煤岩样孔隙空间大幅度减小、渗透率损失的主要原因;破碎样(煤岩样)的强度决定渗透率的应力敏感性,组合煤岩样中煤的比例越大,渗透率的应力敏感性越高,渗透率越小;随着加卸载次数的增加,应力敏感性逐渐减弱。最后,根据实验结果给出了不同加卸载阶段破碎煤岩样的应力-渗透率计算模型。

When the coal-seams are multi-layered,the stress and permeability of the caving zone are disturbed again during the following coal seam mining.Repeated unloading and compaction cause caved coal and rock to break further in the caving zone,which in turn affects the migration of gas in goaf.This paper briefly summarizes prior research on caving zone internal stress,porosity,permeability and other parameters of the process of longwall face advancing.The forecast methods for calculating the stress and permeability of the caved zone during its compaction are listed.On the basis,this paper describes a laboratory experiment of the broken coal and rock in the caving zone of the gob in Huainan coal mine.The laboratory test results imply that the re-crushing,re-arrangement,and compressional deformation of particles in the loading process lead to a drastic drop in the caving zone porosity,which causes the permeability reduction.The permeability sensitivity to stress of broken rock(broken coal)samples was determined by their strength.The greater the proportion of coal samples in the combined coal and rock samples,the higher the permeability stress sensitivity and the smaller the permeability.With the increase of the cyclic times,the stress sensitivity gradually weakened.Based on laboratory experiments,the stress-permeability fitting model of the broken coal and rock in the caving zone during the group coal seam mining is proposed in this paper.