山岭隧道跨断裂带段及洞口段地震响应大型振动台模型试验研究

Large scale shaking table model test on seismic response of mountain tunnel portal section passing through fault zone

为研究地震作用下山岭隧道跨断裂带段及洞口段的动力响应及其破坏机制,以国道318线康定折多山隧道工程为背景,设计并开展隧道长达8 m的大型地震动模拟振动台试验,对比分析处于不同围岩条件中衬砌结构的动力响应规律及其破坏机制,研究结果表明:在本次振动台试验中,隧道衬砌结构的加速度、动土压力以及应变等响应主要受周围围岩条件的影响,其所处的围岩质量越差地震反应越强烈。在三向地震作用下,隧道衬砌结构的PGA放大系数随着地震波幅值的增加逐渐减小,各部位间动土压力和应变差值逐渐增大并进入偏心受力状态,横截面共轭45°为主要受力方向。此外,衬砌结构的纵向破坏由洞口处向深部围岩发展,且各段衬砌具有相同的破坏机制,即破坏过程为自“仰拱→拱脚→拱肩→拱顶”发展。对比分析处于不同围岩条件中衬砌结构的最终破坏形态,洞口和断裂等围岩条件较差段衬砌结构的震害较为严重,且下部结构的震害明显比上部结构严重。因此,在实际工程中需重点关注洞口段和断裂带段衬砌结构的抗震设防,加强衬砌仰拱、拱脚等下部结构的加固设计。

In order to study the dynamic response and failure mechanism of mountain tunnel across fault zone and portal section under earthquake,a large-scale shaking table test was designed and carried out according to the Kangding—Zheduoshan tunnel project.Through this test,the dynamic response and failure mechanism of tunnel lining under different surrounding rock conditions were compared and analyzed.The research results show that:in this shaking table test,the acceleration,dynamic earth pressure and strain responses of tunnel lining were mainly affected by the surrounding rock conditions.The quality of surrounding rock around tunnel lining is poor,and its seismic response is strong.Under the action of three-dimensional seismic wave,the PGA amplification coefficient of tunnel lining decreases gradually with the increase of seismic wave amplitude,and the difference between dynamic earth pressure and strain increases gradually.The tunnel lining is under eccentric stress,and the conjugate 45°of cross section is the main stress direction.In addition,the longitudinal failure of lining structure develops from the portal to the deep surrounding rock,and each section of lining has the same failure mechanism.The failure process develops from“inverted arch→arch foot→arch shoulder→arch crown”.By comparing and analyzing the final failure modes of tunnel lining,it is found that the seismic damage of lining structure in portal section and fault zone section is more serious,and the seismic damage of substructure is obviously more serious than that of superstructure.Therefore,in the same tunnel project,it is necessary to pay attention to the seismic fortification of the mountain tunnel across the fault zone and the portal section,and focus on the seismic design of the lining inverted arch,arch foot and other parts.