隧道仰坡地震动力响应特性振动台模型试验研究

为研究地震作用下山岭隧道仰坡的动力响应特性及仰坡坡体和衬砌结构的相互作用,设计并完成了隧道洞口段大型振动台模型试验。试验结果表明,地震作用下仰坡的加速度反应存在显著的非线性放大效应和趋表效应;当输入地震波幅值超过0.6g时,土体的非线性反应明显增强,加速度放大系数显著降低,表现出放大效应饱和的特性,且沿坡体竖直向上,加速度分布逐渐表现出平均化的趋势;隧道洞口段仰坡水平向动力反应受隧道结构存在的影响较小,可简化为自然边坡进行分析;仰坡的动力失稳是影响衬砌结构安全性的重要因素,当输入地震波幅值较小时,竖直向地震作用下衬砌主要受力部位受力要大于水平向地震作用,当幅值较大时,水平向地震动对衬砌结构的影响则明显大于竖向地震动;均质仰坡的破坏部位主要位于仰坡坡肩至坡面上部,破坏过程表现为地震力诱发-坡肩土体拉裂张开-坡肩土体倾倒崩塌-崩塌的土体沿坡面滑落碰撞-形成碎屑流堆积于坡脚。模型试验的结果能为山岭隧道洞口段的理论分析、计算和设计提供指导和依据。

Shaking table test study of seismic dynamic response of tunnel entrance slope

A large-scale shaking table model test is conducted to study the dynamic behavior of entrance slope and its interaction with lining structure of mountain tunnel under earthquake loading. Test results show that the acceleration response of tunnel entrance slope exhibits obvious amplification effect and surface effect along both vertical and axial directions. Significant nonlinear behavior is observed when the earthquake loading amplitude is larger than 0.6g; and after that, amplification factor decreases with the increase of input loading amplitude and additionally the distribution of acceleration becomes more even in the slope body. It is also found that the dynamic response along axial direction of entrance slope does not affect much by existence of tunnel structure; thus it could be evaluated by treating the entrance slope as a natural slope for simplification. On the other hand, however, the potential instability of entrance slope has much influence on the safety of tunnel structure. When the loading amplitude is relatively small, internal force induced by vertical acceleration is larger than that caused by horizontal acceleration. As the loading amplitude becomes larger, the horizontal component of earthquake plays a dominant role in affecting the lining structure. The failure surface is located at the upper part of entrance slope, especially on the shoulder. The failure process could be described as five steps: (1) earthquake excited; (2) slope shoulder cracked due to tensile failure; (3) the cracked rock of shoulder toppled and collapsed downwards; (4) the collapsed rock fell along the slope and crushed to debris; (5) rock debris accumulated at the slope toe. The experimental result provides valuable basis and guidance for analysis, calculation and design of mountain tunnel portal.