不同孔隙水压条件下完整砂岩剪切力学特性试验研究

Experimental study on shear mechanical properties of complete sandstone under different pore water pressures

利用自主研发的煤岩剪切–渗流耦合试验装置,开展法向应力为2.0 MPa,孔隙水压分别为1.0,2.0和3.0 MPa条件下砂岩剪切破坏试验,同时利用三维立体扫描仪对剪切断裂面进行扫描,运用Matlab软件编写统计参数计算程序,分析不同孔隙水压下的剪切断裂面特征。研究结果表明:(1)孔隙水压对砂岩剪切力学特性具有"软化"效应,孔隙水压越高,砂岩的抗剪强度越低,峰值剪切变形量与峰值法向变形量均越小;(2)孔隙水压越高,试件剪切断裂面各点相对基准剪切面垂直距离的均方根偏差S_q、粗糙度指数S_r以及表面裂纹分形维数D_r等均越小,表明随孔隙水压增大,剪切断裂面粗糙程度降低;(3)通过剪切断裂面裂纹扩展分析发现,在不同孔隙水压条件下的剪切试验过程中,试件表面裂纹的扩展只能反映靠近该表面很小范围的内部裂纹扩展情况,不能等同试件剪切断裂面裂纹的扩展路径。

Based on the self-developed shear-seepage experiments of complete sandstone was carried out under coupling test device for coal rock, the shear failure normal stress of 2.0 MPa, pore water pressures of 1.0, 2.0 and 3.0 MPa respectively. At the same time, the shear fracture surface of different pore water pressures was scanned by the three-dimensional scanner, and it＇s characteristics was analyzed by statistical parameter that was calculated by Matlab software. The results show that： （1） the shear mechanical properties of sandstone will appear ＂softening＂ effection under pore water pressure, and the higher pore water pressure is, the lower shear strength of sandstone is, in addition, the deformations of peak shear and the peak normal are smaller. （2） The root mean square of the vertical distance from all points on the shear fracture surface to the base level, the roughness index and the fractal dimension of surface crack decrease with the increase of the pore water pressure, which indicates that the roughness of shear fracture surface decrease with the pore water pressure rising. （3） Through analysis to crack propagation of shear fracture surfaces, it is found that the crack propagation on specimen＇s surfaces can only reflect inner cracks in small range near the surface instead of whole fracture surface in the process of shear test under different pore water pressures.