中文摘要：

隧道洞口段是隧道抗震设计的薄弱部位,文章从瑞利波动方程出发,推导了洞口段地层在瑞利波作用下的峰值位移、峰值加速度和地层曲率的计算公式,并探讨了洞口段抗震设防长度。分析结果表明：在瑞利波作用下,地层位移、曲率和加速度随隧道埋深的增大而迅速减小,因此当洞口埋深达到一定程度后,地层对隧道的强加位移已很小,无需再设防;现行隧道设计规范规定的洞口段抗震设防长度偏短,应延长。最后,结合汶川地震隧道洞口段破坏长度,进行了分析验证,分析结论可供隧道抗震设计、灾后重建和今后有关规范修订参考。

英文摘要：

Tunnel portals are the weak point in the seismic design of tunnels.Based on wave equations of Rayleigh waves,the calculation formula of displacment,acceleration and curvature of the ground are gained,and the seismic fortification length of tunnel portals are discussed.The results show that 1） the displacment,acceleration and curvature of the ground decreased rapidly as the burial depth increased under the Rayleigh wave action;2） seismic fortification length should be prolonged.In the end,seismic fortification length proposed for tunnel portal is verified by the damage of tunnel portals in the Wenchuan earthquake.The content in the paper may be as a reference to seismic design of tunnels,reconstruction of disarster areas and revision of corresponding codes and regulations.