层状大理岩卸荷力学特性试验研究

 以锦屏一级水电站地下厂房实际应力环境为基础，利用MTS815 Flex Test GT岩石力学试验系统，对该厂房区域典型层状大理岩开展常规三轴加、卸荷破坏试验研究。研究成果表明：平行层理面压缩时，卸荷试验得到的抗剪断、抗剪强度参数较加载试验得到的c，j 值低，残余内摩擦角jr值却较高；相同卸荷条件下，垂直层理面压缩得到的抗剪断、抗剪强度参数较平行层理面压缩得到的c，j 高，jr值却较低；卸荷条件下岩样的破坏是其向卸荷方向的强烈扩容所致，峰值强度后继续卸荷对岩石峰后承载力有显著的弱化作用；试验得到的各组弹性模量大致随围压增加而增加，而峰值应力对应的变形模量则反之，单个岩样在卸荷试验中，变形模量大致随围压卸荷而降低，垂直层理面压缩得到的变形模量较平行层理面压缩的高20%～51%，侧胀系数m 的变化规律则反之，前者较后者的低3%～12%；在相同卸荷条件下，平行层理面压缩时，岩石更易发生破坏，而垂直层理面压缩时，大理岩的脆性变形特征更显著。这些结论揭示了层状大理岩的卸荷力学特性，对解决工程实际问题有重要的参考价值。

EXPERIMENTAL STUDY OF MECHANICAL PROPERTIES OF LAYERED MARBLE UNDER UNLOADING CONDITION

The layered marble samples are collected from the underground powerhouse of Jinping I hydropower station which is a large-scale national key project. To simulate the excavation unloading effect,a series of triaxial unloading tests are carried out on MTS815 Flex Test GT rock mechanics test system,and a series of triaxial loading tests for comparison are also performed. The results show that there are obvious differences among mechanical properties of layered marble with different axial compression directions. When the axial compression parallels bedding plane,the shear strength parameters c and φ decline but residual strength parameter φ_r increases under unloading condition. When the axial compression is perpendicular to bedding plane,the shear strength parameters c and φ increase but residual strength parameter φ_r declines compared with the results of axial compression paralleling bedding plane under the same unloading condition. The prompt lateral expansion causes the failures of these rock samples and confining pressure unloading after peak strength significantly weakens their bearing capacities. The elastic modulus increases approximately with initial confining pressure increasing in loading and unloading cases,but the rule of deformation modulus at peak strength is reverse. For a single sample under unloading condition,whether axial compression is perpendicular to or parallels the bedding plane,the deformation modulus always decreases with confining pressure declining;and the value of the former is 20%–51% higher than that of the latter;but the lateral expansion ratio(μ) of the former is 3%–12% lower than that of the latter;and the rule is reverse. Under the same unloading condition,axial compression paralleling bedding plane is more easily to cause the failure of rock samples than axial compression perpendicular to bedding plane;but the latter samples are of more obvious brittleness. These conclusions reveal the unloading properties of layered marble and offer important reference to solve practical engineering problems.