等向压缩及偏压加载下锦屏大理岩变形特性研究

Deformation behavior of Jinping marble under isotropic compression and deviatoric stress loading conditions

以中国锦屏地下实验室工程T_(2b)大理岩为研究对象,开展了等向压缩(σ_1=σ_2=σ_3)试验及不同围压下的三轴偏压(σ_1-σ_3)加载试验,分析讨论了大理岩等向压缩体积变形特点、围压对峰后变形行为及峰前渐进性变形破坏过程的影响。试验结果表明:大理岩的等向压缩体积变形在不同围压范围内经历了一个线性-非线性-线性的变化过程。等向压缩体变曲线上存在一个拐点(敏感应力),该点的围压能在一定程度上反映其应力历史。偏压加载时峰后变形表现为脆性-半脆性-延性转化特征,峰值强度随围压变化与等向压缩体变曲线斜率发生变化的转换围压是一致的。围压对渐进性破坏过程各个阶段均会产生一定影响,除偏差闭合应力阈值外,其余各特征偏应力阈值均随围压近似呈线性增加关系。在等向压缩和偏压加载时出现了2次裂隙闭合过程。试验成果对进一步研究硬岩的变形破坏机制、防治深部地下工程灾害具有一定参考价值。

Isotropic compression and conventional triaxial compression experiments are performed on the T_（2b） marble samples taken from Jinping underground laboratory, China, and some issues related to the isotropic compression deformation characteristics, the effect of confining pressure on the post-peak behavior and the pre-peak progressive failure process have been analyzed and discussed. The test results show that the volumetric strain under isotropic compression presents a linear-nonlinear-linear change when subjected to a confining pressure increase. An apparent volume change inflection point（sensitive stress） is observed, which can be related to stress history. There is a brittle-semi brittle-ductile transition trend with increasing confining pressure in the results of the conventional triaxial tests, and the change of the strength is consistent with the change of the isotropic compression curves which is in isotropic pressure vs. volumetric strain plot. Furthermore, the increased confining pressure has an effect on each stage of the progressive failure process, and other stress thresholds of the marble increase approximately linearly with the confining pressure except the crack closure deviatoric stress threshold. The initial crack closure process of the marble occurs twice, one under isotropic compression and the other under the deviatoric stress loading condition. The above results of Jinping T2 b marble is valuable for achieving a better understanding the rock failure mechanism and preventing disasters in deep underground engineering.