山岭隧道洞口段地震响应振动台模型试验研究

Shaking table test for seismic response in portal section of mountain tunnel

通过对已有震害的调查发现,洞口段为山岭隧道抗震的薄弱环节,容易发生边坡失稳及衬砌结构的损坏。对隧道洞口段进行了大型振动台模型试验研究。研究结果表明:由于洞口仰坡临空面的存在,在距离洞口一定范围内会出现加速度的"放大效应",这种"放大效应"会导致衬砌间的非一致振动;应变结果显示:衬砌结构主要以横向受力为主,地震附加应力主要集中在拱肩和拱脚,这些部位为衬砌结构抗震的薄弱环节,试验中距洞口一定距离处的衬砌结构最先破坏,故洞口加速度的"放大效应"并不代表衬砌结构地震反应内力的放大,洞口处衬砌结构惯性力不是结构地震反应附加内力的主导部分;洞口仰坡的坡面位移随着高程的增大呈抛物线形增长,衬砌结构整体变形为椭圆形,变形较大的位置为拱肩和拱脚;随着地震波的逐级加载,洞口仰坡发生推动式滑坡,从而引起衬砌结构的破坏,施工缝的存在消耗围岩变形对衬砌结构产生的附加内力,有助于衬砌结构抗震。试验研究结论可供软弱围岩下山岭隧道洞口段的抗震设计参考。

By in-situ investigation, it is found that portal sections of mountain tunnels are the weaker parts of mountain tunnel, during earthquakes, which leads to slope unstability and lining damages. Large scale shaking table model tests were performed on tunnel portal parts. Results show that an amplification effect of acceleration exists at the area with some distance from the entrance of the tunnel. This effect may produce non - uniform vibration along the lining. The analysis of the strain show that the tunnel lining structure is mainly subjected to transverse stress. And seismic additional stress mainly concentrated at arch waist and arch feet, which could be seen as weak parts in seis- mic design of lining structure. During the test, lining at the area with some distance from the entrance of the tunnel damaged first. And so such amplification effect did not result in greater inner force in tunnel structure. Thus the effects of inertial force on structure inner force is rather small for tunnel portal parts. Displacement of slope surface at tunnel portal section increases according to parabolic law with the slope height. Lining structure is deformed into oval, of which the biggest deformation happens at the arch waist and arch feet. With stepwise loading of seismic wave, a pushed type sliding happens at the tunnel portal section, which results in tunnel structure damages. Exist- ence of construction joints consumes part of additional internal force arising from deformation of surrounding rock, which is of advantage for anti-seismic performance of lining structure. Test results may give a reference to seismic design of tunnel portal section in mountain tunnels in weak surrounding rock.