煤体固液耦合的结构及渗透性演变规律

为了研究煤层固液耦合和渗透水压力(水力梯度)作用下的结构改造及渗透性演变规律,在MTS 815.02电液伺服岩石力学试验系统上采用瞬态压力脉冲法进行了煤体全应力应变过程中的渗透性测试。试验结果表明,煤体的渗透性与其内部结构密切相关,在全应力应变过程,煤体渗透性的演变与其内部裂隙的变化趋势一致。在应变软化至峰值强度的24.98%时,煤体渗透性达15.69×10-13cm/s,分别是弹性阶段和峰值时的79.30倍和16.34倍。在固液耦合不产生损伤的条件下,瞬态渗透系数整体与水力梯度成正比关系。渗透水压力可引起结构面的错动闭合或导致破裂碎屑集聚堵塞渗流通道。当煤样变形进入到弹塑性阶段以后,瞬态渗透系数随时间延长先整体降低,降低到一定值时突然急剧增大至一定峰值,然后再逐渐降低并趋于稳定。且煤样由弹塑性经塑性至破坏(残余强度)阶段,中间突变的峰值与初始瞬态渗透系数的差值越来越小,出现中间突变峰值所需时间越来越长。采用瞬态压力脉冲法测量评价岩石的渗透性时,应采用上下水压差第一次趋于稳定时的数据来计算其渗透系数。

Evolution Law of the Structure and Permeability for Coal Under Solid-Liquid Coupling

To investigate the structure transformation and permeability evolution law of coal seam un-der the effect of solid-liquid coupling and seepage water pressure(hydraulic gradient),the permeability test of coal during the overall stress-strain process has been carried out on MTS 815.02 elec-tro-hydraulic servo rock mechanics test system with the method of transient pressure pulse.The test re-sults show that the coal permeability is closely related to its internal structure,and the permeability evolution is consistent with its variation tendency of internal fractures in the overall stress-strain process.When the strain softening is 24.98 percent of the peak strength,the coal permeability reaches to 15.69×10-13cm/s,which is 79.30 and 16.34 times of that in elastic stage and peak value,respectively.When the solid-liquid coupling doesn’t produce damage,the transient permeability coefficient is proportional to hydraulic gradient on the whole,and the seepage water pressure can cause dislocation and closure to structural planes or make rupture debris gather and block up seepage channel.After the deformation of coal sample enters into elastic-plastic stage,the transient permeability coefficient first decreases with time on the whole and increases rapidly to a certain peak value after it decreases to a certain value,then,it gradually decreases again and tends to be stable.In addition,when the coal sample goes from elas-tic-plastic stage,plastic stage to failure(residual strength) stage,the difference between the mutations peak and initial transient permeability coefficient becomes smaller and smaller,and the emergence of middle mutations peak needs longer and longer time.Moreover,by using transient pressure pulse method to measure and evaluate the rock permeability,the data should be adopted when the upper and lower water pressure difference becomes stable at the first time,to calculate the permeability.