加卸载条件下煤岩变形特性与渗透特征的试验研究

Experimental study of coal deformation and permeability characteristics under loading-unloading conditions

以原煤为研究对象,利用自主研制的含瓦斯煤热流固耦合三轴伺服渗流试验系统,采用加轴压、卸围压的应力控制方式开展煤岩加卸载试验,分析加卸载条件下煤岩变形特性和渗透特征的演化规律。研究结果表明:①加卸载试验峰值强度明显低于常规三轴压缩试验峰值强度,在加卸载过程中,主应力差有一个明显增加趋势,卸载第2阶段速率越大,其曲线斜率也越大,但峰值强度越小,对应的径向应变ε3、体积应变εV增加速率也越快,而到峰值后破坏阶段,均呈下降趋势。②加卸载过程中,煤岩渗透率、应力差与应变关系可以分为3个阶段,初始压密和屈服阶段、屈服后阶段、破坏失稳阶段。试件达到峰值后瓦斯渗透率出现突然小幅度上升,持续一段时间后,渗透率出现急剧陡增趋势。③煤岩渗透率的变化与煤岩的变形损伤演化过程密切相关,渗透率随变形的增大均呈二次多项式函数递增。

Making raw coal as research objects, used domestic-developed triaxial servo-controlled seepage equipment for thermo-fluid-solid coupling of coal containing methane, with one pressure control mode of increasing the axial com- pression and unloading confining pressure to carry out coal and rock loading and unloading test, and analyzed the evo- lution of coal deformation properties and permeability characteristics under loading and unloading conditions. Results show that coal peak intensity under loading and unloading conditions is significantly lower than that under conventional triaxial compression test. The principal stress difference shows an apparently increasing trend during experimental process. The bigger the rate of the second unloading phase is, the greater the curve slope becomes, correspondingly, the faster the radial strain and volumetric strain increases, whereas, the smaller the peak intensity becomes. At the failure stage after peak value, both radial strain and volumetric strain decrease. Relations between coal permeability, principal stress difference and strain can be divided into three stages respectively, initial compaction and yield phase, the stage after yield phase, and failure stage. After the peak, coal permeability showed a sudden small increase, which once again appeared dramatically sharp increase after some time. Changes of coal permeability are closely related to the coal de- formation damage evolution, and the relation between them can be expressed by a quadratic polynomial function.