川西北茂县群千枚岩各向异性力学特性

Anisotropically mechanical characteristics of Maoxian group phyllite in northwest of Sichuan province

利用MTS815Teststar岩石力学试验系统,对川西北茂县群千枚岩开展单轴和三轴试验,研究千枚岩各向异性力学特性。研究结果表明:千枚岩在达到峰值强度50%以前就普遍出现很大的变形和局部破坏,表明围岩产生大变形或出现早期扩容并不意味着其丧失承载能力,如及时进行针对性支护或加强围岩保护仍具有较强的强度。损伤扩容是千枚岩变形破坏的典型特征,并对变形产生不同的影响,横向应变对损伤扩容比轴向应变更敏感,能更灵敏地反映岩石材料内部的屈服、弱化。千枚岩各向异性随含水率与围压水平表现出不同的变化规律,强度各向异性随含水率和围压水平提高而降低,弹性模量和泊松比则与加载方向和转化围压有关。不同含水状态下干燥千枚岩的单轴抗压强度各向异性最为显著,大部分千枚岩的强度各向异性率在0.80以下,其中绢云母千枚岩最强,为0.48,其强弱对比依次为绢云母千枚岩、绿泥石千枚岩、石英千枚岩、炭质千枚岩。千枚岩表现出不同的破坏模式,并随围压或含水率的增加而变化;剪切机制单独控制着各向异性力学特性,千枚岩统一沿软弱面剪切破坏。

This study aims to investigate the anisotropic characteristics of phyllite in Maoxian group from the northwest of Sichuan province in China. A series of uniaxial and triaxial compressive tests is conducted on phyllite samples by using the MTS815Teststar rock mechanics testing system. Experimental results show that the large deformation and partial failure generally appear before samples reach half of their peak strengths. However, the occurrences of large deformation or initial dilatancy do not indicate that rock completely loses its bearing capacity. If the targeted support or protection can be applied on surrounding rock in time, rock strength is still strong. Damage dilation is regarded as a typical deformation and failure characteristic of phyllite. Furthermore, it affects lateral deformation more easily than axial deformation. Thus, lateral deformation can reflect rock yield or weakening more sensitively. Results show that the anisotropy of rock strength decreases with increasing water content and confining pressure. Moreover, Young＇s modulus and Poisson＇s ratio vary with the loading direction and translated-confining pressure. From the obtained results of phyllite at different water contents, the strength of phyllite under dry condition presents the most obvious anisotropic characteristics in uniaxial compressive tests. It is found that the anisotropic ratios of compressive strength are mainly below 0.8. Especially, sericite phyllite exhibits the strongest anisotropy with a ratio of 0.48, and the following anisotropic orders from strong to weak are sericite phyllite, chlorite phyllite, quartz phyllite, and carbonaceous phyllite. Moreover, there are different failure modes of phyllite, which also change with the increase of confining pressure and water content. Shear failure occurred uniformly along the weak planes, which indicates that the anisotropic mechanical characteristics of phyllite are controlled by shear mechanism independently.