不同仰坡度数的山岭隧道洞口段动力响应振动台试验研究

Large-scale shaking table test for dynamic response in portal section of mountain tunnel with different gradients of upward slope

首先介绍试验装置、模型相似比、试验模型箱等,然后对围岩与隧道结构的加速度响应、衬砌的位移和应变响应以及仰坡坡面的破坏情况进行分析。分析表明,由于洞口临空面的存在,隧道洞口处会出现加速度和位移的放大效应,不同的仰坡角度下均符合该特性,但随着仰坡坡度的增加,放大效应会逐渐减弱。在振动过程中衬砌横断面承受循环的拉压荷载作用,两侧的拱肩和拱脚位置出现较大的地震附加弯矩,受力特性与仰坡坡度无关,但地震附加弯矩会随着覆土厚度和结构惯性力的增加而增大;随着仰坡坡度的增加,结构与围岩在洞口处的相互作用会逐渐减弱,仰坡坡面的破坏形式分别为坡面的局部崩塌、衬砌顶部的大面积滑塌和坡顶的高位滑塌,均为浅层破坏,但坡面坍塌围岩会不同程度的掩埋洞口,对隧道的正常使用造成严重的影响,故应对洞口仰坡进行重点设防。分析结果对于合理认识山岭隧道洞口段地震响应特征具有积极作用,可供隧道实际工程设计和施工的抗震设防参考。

The tests arrangements are systematically introduced firstly, including test facilities, similar ratios, modelling materials, model cases and so on. Then, the test results including accelerations of surrounding rock and tunnel structure, laws of strains and deformations of structures, failure features of upward slope. The analysis results show that: an amplified effect of acceleration and displacements of tunnel structures exist at the area which is of some distance from the entrance of the tunnel. There is not much differences in the law of the amplification effect for different gradients of upward slope. The amplification effect decreases as the gradient of upward slope increases. The analysis of the strain show that the tunnel structure is mainly subjected to transverse stress. A cycling load of tension and pressure acts on the cross-section of the tunnel which result in additional seismic bending moment on arch waist and arch feet, which could be seen as weak parts in seismic design of lining structure. The mechanical characteristics of lining has no relation with the gradient of upward slope. The additional moment is proportional to soil thickness and the inertia force of lining. As the gradient of upward slope increases, the soil-structure interaction effect is gradually weakened; and the failure modes of the slope are different, which include local slope collapse, large slump at the top of the lining, highstand sliding. Both of them are all the surface failure. But the tunnel openings are usually partially or completely buried, which severely affect the normal use of tunnel. Tests results provide references for seismic design of tunnel portal section in mountain tunnels.