深埋大理岩卸荷力学特性的试验研究

Experimental Research on Mechanical Properties of Deeply Buried Marble Under Unloading Conditions

为探讨深埋大理岩在不同应力路径下力学性质的差异,揭示卸荷应力路径对岩石力学性质的影响,对取自锦屏二级深埋引水隧洞的浅灰色大理岩进行了常规三轴和2种应力路径的卸荷三轴试验研究,得到了卸荷应力状态下,大理岩破坏时的纵横应变小于常规三轴压缩应力状态得到的结果,且其变形具有由延性变形向脆性变形转化的特征。不同应力路径下大理岩的变形模量和泊松比与围压均有良好的线性关系,但卸荷应力状态下的变形模量较常规三轴压缩应力状态下的小,泊松比则相反。卸荷状态下大理岩的破坏面更为粗糙,其内聚力较三轴压缩状态下的内聚力下降了36.4%,而内摩擦角增加了35.4%;在45 MPa正应力范围内,卸荷应力状态下的抗剪强度低于常规三轴压缩状态下的抗剪强度,卸荷应力状态下更易导致岩石发生破坏。

To discuss the difference of mechanical behavior of marble buried deeply in high stress caused by different stress paths and reveal the influence of unloading on rocks＇ mechanical properties, a series of triaxial tests under loading and unloading conditions were carried out on the marble samples from the tunnel of Jinping Secondary Hydropower Project. The results showed that when marble is bro- ken, the vertical and horizontal strain under unloading condition are smaller than that under triaxial compression tests, and the brittle features of rocks are more conspicuous under unloading condition. The secant modulus and Poisson ratio have good linear relationship with confining pressure in different stress paths. The secant modulus under unloading condition is smaller than that under triaxial com- pression test, but Poisson ratio is on the contrary. The failure face of marble is more rough under unloading condition, and the cohesion c decreases 36.4% while the internal friction angle ~o increases 35.4% relatively with the loading tests. The shear strength in unloading condition is lower than that in loading condition when normal stress is below 45 MPa, and damage occurs more. These results showed that the influence of unloading should be considered fully during the excavation of deep underground engineering.