深埋洞室开挖瞬态卸荷诱发振动的衰减规律

Attenuation law of vibration induced by transient unloading during excavation of deep caverns

深埋洞室爆破开挖过程中围岩初始地应力的瞬态卸荷会诱发振动。针对圆形隧洞开挖,分析了地应力瞬态卸荷过程中围岩应变能、动能、径向应力做功3者之间的平衡机制,并采用量纲分析,建立了基于开挖岩体应变能的瞬态卸荷诱发振动衰减公式。结合锦屏二级引水隧洞和瀑布沟地下主厂房爆破开挖实例,开展了瞬态卸荷诱发振动的识别分离,并分析了诱发振动的衰减规律。研究表明:地应力瞬态卸荷诱发振动的峰值与被开挖岩体应变能密度的二次方根成正比,且开挖卸荷体积越大,诱发振动越强烈;与Lu-Hustrulid衰减公式相比,新衰减公式应用范围更广,使用精度更高。

During drilling and blasting excavations of deep caverns, the transient unloading of in-situ stress on the excavation boundary can induce vibrations in surrounding rock mass. For circular tunnel excavation, the balance mechanism of strain energy, kinetic energy and work done by radical stress during the process of the transient unloading of in-situ stress is analyzed, then a new attenuation formula is established to analyze the attenuation law of vibrations induced by the transient unloading of in-situ stress based on the strain energy of excavated rock mass with the tool of unit analysis. Case studies of Jinping II and Pubugou hydropower stations are presented to show how to identify and separate the vibrations induced by the transient unloading of in-situ stress from the monitored vibration signals. Studies indicate that the amplitudes of vibrations induced by the transient unloading of in-situ stress are proportional to the square root of strain energy density of excavated rock mass, and the bigger volume of excavated rock mass is, the intenser vibrations are induced by the transient unloading of in-situ stress. Compared with the existing attenuation formula proposed by Lu and Hustrulid, the new attenuation formula has a wider range of application and higher precision.