地震作用下立体交叉下穿隧道动力响应振动台试验研究

随着国家路网的不断建设与规划,大量铁路隧道或公路隧道近接平行、交叉等工程现象不断涌现,受地形、地质条件以及线路走向等因素的限制,隧道近接交叉的工程问题越来越复杂。以立体交叉草莓沟1#隧道和盘道岭隧道为例,着重选取盘道岭隧道(下穿隧道)为研究对象进行振动台试验,重点分析受上跨隧道影响,超小净间距小角度立体交叉下穿隧道拱顶、仰拱断面的加速度和应变动力响应特征。在此基础上,以该场区沿线地震动峰值加速度0.15 g加载工况为依据,对环向最大地震应变规律进行分析,根据有效频率加速度计的范围和输入的功率谱振幅,利用SPECTE反应谱分析程序,对交叉中心拱顶和仰拱位置的加速度反应谱的分布规律进行对比分析和研究。试验结果表明:(1)受立体交叉隧道空间位置影响,超小净间距小角度立体交叉下穿隧道拱顶加速度时程和频谱较仰拱整体响应大,受振有效持续时间较长,空间分布表现为拱顶幅值反响突出的特点。(2)拱顶峰值加速度响应具有叠加效应,其加速度峰值比率表现为明显的非线性、非平稳性增大的特点,地震烈度越高,应变响应越大,拱顶破坏模式表现为交叉段–河侧–山侧的传递演化形式。(3)随着输入地震波增强,隧道仰拱动应变和加速度峰值比率增长变化表现出局部变化性质。(4)隧道围岩对地震波的高频段存在滤波作用,对隧道结构影响较大卓越主频段集中在1~10和11~20 Hz两个低频段,主频段卓越频率的取值为5,12.5 Hz。(5)不同地震烈度时,各特征点处应变峰值大小依次为:拱顶>仰拱>河侧拱腰>山侧拱腰,加速度响应的卓越频率与速度、位移响应三者之间受基频和阻尼影响,从而产生时间和空间等的差异变化,宜鼓励设计过程中提高该隧道的阻尼结构性能,阻尼比建议值取为20%。研究结果可为立体交叉隧道的抗震设计提供一定的理论指导。

Shaking table test study on dynamic responses of underpass tunnels under earthquake

With the continuous construction and planning of national road networks,a large number of close parallel or cross railway and highway tunnels has been emerging. Due to the limitations of topography,geological conditions and line strike,the engineering problems of near junction tunnels are more and more complicated. In this paper,taking the 3 D crossing Strawberry Channel 1# and Pandaoling Tunnel as examples,especially the Pandaoling Tunnel(underpass tunnel) for the shaking table test,the acceleration and strain dynamic responses of the vault and inverted arch cross-section of ultra-small net spacing and small-angle underpass tunnels affected by the upper-span tunnel were analyzed. Specifically,the maximum seismic strain in the hoop direction was evaluated under the loading condition of 0.15 g peak acceleration of ground motion along the field,and according to the range of the effective frequency accelerometer and the input power spectrum amplitude and using the SPECTE response spectrum analysis program,the distributions of the acceleration response spectrum of the vault and inverted arch at the intersection central were compared. The results show that,affected by the spatial position of the 3 D cross tunnel,the acceleration time history and spectrum of the ultra-small net spacing and small angle underpass tunnel are larger than the overall response of the inverted arch,the effective duration of vibration is longer and the spatial distribution is characterized by the prominent amplitude response of the arch. The peak acceleration response of the vault has a superposition effect and the peak acceleration ratio is obviously nonlinear and non-stationary. The higher the earthquake intensity is,the greater the strain response will be. The failure of the vault shows a transfer evolution form from the cross section to the river side then to the mountain side. With increasing the input seismic wave,the increases of the dynamic strain and the peak acceleration ratio of the inverted arch show local changes. The surrounding rock of the tunnel has filtering effect on the high frequency band of the seismic wave. The predominant main frequency markedly influencing the tunnel structure concentrates in two low frequency band of 1﹣10 Hz and 11﹣20 Hz,and the values of the predominant frequency corresponding to the maximum acceleration response of the vault and inverted arch are respectively 5 Hz and 12.5 Hz. For different seismic intensities,the peak strain at the vault are largest,followed by the inverted arch,and the arch waists of the riverside and the mountainside in turn. The predominant frequency of the acceleration response and the responses of the velocity and the displacement are affected by the base frequency and the damping,resulting in difference in time and space. It is suggested that he performance of the damping structure of the tunnel during the design process should be improved and the recommended damping ratio is 20%. The research results can provide certain theoretical guidance for the seismic design of 3 D cross tunnels.