高应力下岩石非线性强度特性的试验验证

 深埋工程岩体开挖后围岩的强度特性表现出明显的非线性特征。基于室内岩石三轴加载及卸荷力学试验成果，对高应力下岩石的非线性强度特性予以验证，并开展高应力下应力路径对强度参数影响规律研究。采用已有的二次抛物线型、双曲线型、幂函数型等型式的包络线来研究强度特征的非线性，结果表明，幂函数型Mohr准则能够作为在高应力加载和卸荷应力路径下的岩石破坏的强度判据。在低围压下(＜10 MPa)，三轴卸围压破坏强度要小于常规三轴强度；而在高围压下，前者略高于后者。内摩擦角的正切值与等效法向应力的函数关系表明岩样的实际内摩擦角并不是一个不变值，具有幂函数关系的非线性特征，在低应力下卸载破坏内摩擦角要比常规三轴压缩剪切内摩擦角略大，在高应力下则相反；根据Mohr准则中内摩擦角与理论破裂角之间的关系，随着应力增加它们的破裂角均呈非线性衰减并趋向π/4。

EXPERIMENTAL VALIDATION OF NONLINEAR STRENGTH PROPERTY OF ROCK UNDER HIGH GEOSTRESS

The strength characteristics of deep rock mass exhibit distinctly nonlinear response to excavation. Based on triaxial compressive tests and unloading confining pressure tests results under high stress in laboratory,the behaving nonlinear strength property is validated. Moreover,the nonlinear strength parameters' change laws by loading and unloading paths of rock failure are brought into research. The quadratic parabola,hypobola,and power types of envelope functions are employed to present nonlinear strength characteristics;and the results reveal that the power type of Mohr criterion can favourably describe the strength property of rock under high geostress in loading path as well as unloading path. The triaxial unloading failure strength is usually less than that under triaxial compressive strength at low stress level,and reversed at higher stress level. According to relationship of internal friction angle with equivalent normal stress,the intrinsic friction angle is not constant,which takes on power functional type of nonlinear characteristics and attenuates gradually to angle of π/4.