不同粒度砂岩力学和渗透特性试验研究

为探讨砂岩粒度对力学行为和渗透特性的影响,利用MTS815 Flex Test GT岩石力学试验系统,对取自同一工程的粗粒砂岩、中粒砂岩和细粒砂岩进行常规三轴试验和三轴压缩全过程渗透试验。研究表明:随着粒度减小,砂岩抗压强度及抗剪强度参数c和φ均增大;渗透水压作用下砂岩强度降低5.15%~24.66%。渗透率变化规律与变形变化特征呈阶段对应:线弹性阶段砂岩内部孔隙被压密,渗透率降低;弹塑性阶段渗透率先是缓慢增加然后急剧上升,在峰后达到最大值;峰后继续破坏阶段渗透率又呈逐渐降低特征。相同粒度砂岩的渗透性随围压增加而降低,且不同围压下渗透率可拟合成线性函数;相同围压下不同粒度砂岩渗透率整体特征表现为:粗粒砂岩渗透率K约为中粒砂岩的105倍,中粒砂岩渗透率K约为细粒砂岩的10倍。

Experimental study on mechanical and permeability properties of sandstone with different granularities

In order to investigate and reveal the influence of granularity on mechanical behavior and permeability characteristics of sandstone, the conventional triaxial tests and triaxial compression and penetration tests are conducted on coarse sandstone, medium sandstone and fine sandstone of a project by using the MTS815 Flex Test GT rock mechanics test system. The researches show that the strength of sandstone and the parameters of shear strength, cohesion c and internal friction angle φ, increase with the decrease of granularity. The strength of sandstone has a decrease of the range between 5.15% and 24.66%. The permeability varies according to the characteristics of deformation: at the elastic stage, the holes inside the sandstone are compacted and the permeability decreases; at the elastic-plastic stage, the permeability increases slowly at first, and then moves up sharply and reaches the maximum value at the post-peak; finally, permeability decreases. The permeability of sandstone with the same granularity decreases with the increase of confining pressure, and the permeabilities of all samples under different confining pressures can be drawn as a linear function. Under the same confining pressure, there is a magnitude difference between the permeabilities of sandstone with different granularities. As for the overall performance of permeability, the permeability of the coarse sandstone is about 10⁵ times that of the medium sandstone, and the permeability of the medium sandstone is about 10 times that of the fine sandstone.