变质砂岩卸围压破坏特征试验研究

山岭隧道工程高地应力岩爆现象的发生受多种因素的影响,其中岩石卸围压过程中的破坏特性是其重要的判别标志之一。本文结合二广高速公路茅田界隧道隧址变质砂岩常规三轴试验不同围压条件下峰前卸围压试验,开展岩石破坏的全过程实验研究,并结合破裂过程的声发射特征探讨了岩石的变形破坏特征,初步分析了卸载破坏诱发岩爆机理基本特征。研究结果表明:随着围压不断的增加,变质砂岩变形特性表现出低围压下的脆性向高围压下塑性的转换,说明围压的增加抑制了岩样的破坏,提高了岩样的承载能力。在相同围压条件下,较快的卸载速率使岩样破坏时释放的能量更小,说明岩样破坏前所能储存的极限储存能更少,这样岩爆就会更容易发生。此外,变质砂岩破坏初期是以张性破坏为主,峰前卸围压,高地应力下变质砂岩表现出张剪性破坏特征,且岩样表现出的脆性随围压强度增大而减小。

Testing on Unloading Confining Pressure for Characteristics of the Metamorphic Sandstone

Rock burst is a dynamic phenomenon and can be induced by multiple factors in excavation unloading of underground engineering. The process of unloading confining pressure can identify the characteristics of rock fracture. Based on the analysis of actual stress states on surrounding rocks, conventional triaxial and different unloading confining stress tests were conducted after the peak strength of metamorphic sandstones in the Maotianjie tunnel site of the ErGuang highway. The process of rock failure was studied with the monitoring of acoustic emission, while characteristics of rock fracture were analyzed in case of rock bursting. The experiment results show that brittle facture can be identified in a lower confining pressure, and the plastic deformation was the main feature after the increasing of confining pressures. It can be concluded that the capacity of metamorphic sandstone was increased due to the increasing of confining pressures. Meanwhile, a rapid unloading rate can make less energy released for rock fracture, which can induce the occurrence of rock bursting. Furthermore, the metamorphic sandstone can be presented as tensile shear failure in case of a high earth stress if the confining pressure was unloaded after the peak strength, and the brittleness can decrease with the increasing of confining pressures.