层状岩体在三轴加载下的扩容及塑性应变特性

Dilatancy and plastic strain characteristics of layered rock mass under triaxial compressive test

为研究层状岩体在三轴加载下的扩容及塑性应变特性,选取具有典型层理构造的千枚岩为研究对象,制作倾角为0°、30°、45°、90°标准岩样,采用MTS815试验系统进行三轴加载试验,定义了塑性应变比以研究轴向与环向裂隙的发展速度。结果表明:千枚岩应力-应变曲线5个典型区段及特征应力与围压和层理倾角存在明显的相关性;千枚岩扩容起点对应的体应变随着围压的升高而减小,扩容起点对应的轴向应变和体应变随着倾角的增大而减小;不同层理倾角千枚岩长期黏聚力普遍大于峰值黏聚力,长期摩擦角普遍小于峰值摩擦角;较低围压水平下轴向裂隙的发展速度比环向裂隙的发展速度更快,较高围压水平下环向裂隙的发展速度随着偏应力增大而显著变快。

In order to study the dilatancy and plastic strain characteristics of layered rock,the phyllite was made into samples with bedding angle of 0 degree,30 degree,45 degree,and 90 degree.The experi⁃ments were conducted on MTS815 servo-controlled test machine,a coefficient is defined for qualitative anal⁃ysis of the axial and circumferential crack named plastic strain ratio,the results show that the five typical sections and characteristic stresses of the phyllite stress-strain curve change with the change of confining pressure and loading direction,which is determined by the force mechanism of phyllite.The volumetric strain corresponding to the dilatancy point of the phyllite is reduced as the confining pressure increases.Be⁃sides,as the inclination increases,the axial strain and volumetric strain corresponding to the dilatancy point decrease.Regardless of any bedding angle,the long-term cohesion of phyllite is generally greater than the peak cohesion,and the long-term friction angle is generally less than the peak friction angle.The development speed of axial fracture is faster than that of circumferential fracture under low confining pres⁃sure,and the development speed of circumferential fracture under high confining pressure is significantly faster with the increase of deviatoric stress.