软土隧道基于地震响应的输入地震动排序

为探讨“最不利地震动”概念在地下结构抗震设计中的适用性，以软土地铁区间隧道为对象建立相应的地层-结构动力分析模型。以直径变形率为分析指标，基于动力时程方法研究18条不同输入地震动作用下隧道结构动力响应的分布及差异性，得出基于隧道地震响应的输入地震动排序，并通过调幅手段对比分析了地面峰值加速度（PGA）和隧道埋深变化对隧道结构地震动响应排序的影响规律。最后，评价了不同输入地震动参数，包括峰值加速度、峰值速度、峰值位移、绝对累积速度（CAV）和阿里亚斯（Arias）强度（I_A）与隧道地震响应之间的相关性。分析结果表明:① 随着PGA从0.5 m/s2增加到2 m/s2，地震动排序发生明显变化，并且不同输入地震动引起的隧道地震响应差异显著提高，最不利地震动引起的直径变形率与平均值的比值从1.1增加到1.9；② 隧道从浅埋到深埋的过程中，地震动排序结果基本保持不变；③ PGA为2 m/s2时，隧道地震响应与基岩面峰值速度（PBV）的相关性最好，相关系数达到0.94，其次是与基岩面峰值位移（PBD）和I_A，相关系数分别为0.62和0.48，相关性最差的是基岩面峰值加速度（PBA）和CAV，相关系数仅为0.37和0.22。研究结论可为今后软土隧道的输入地震动选择提供科学依据。 

Ranking the seismic input motion based on seismic response of soft soil tunnels

The selection of input motion is of most importance in seismic design and analysis of underground structures. In recent years, the concept of “the most unfavorable ground motion” has been widely studied and applied in the field of seismic design for surface structures. However, there is no research on ranking the seismic input motion based on the seismic response of underground structures. To explore the applicability of the concept of “the most unfavorable ground motion” for the seismic design of underground structures, a circular tunnel in soft soil is taken as the research object, and the corresponding soil-structure dynamic analysis modelis established. Taking the ovaling deformation rate of the circular liner as the critical index of tunnel responses, the distribution as well as the difference of dynamic responses of the tunnel structure under excitations of 18 different input motions are studied with the dynamic time-history method, and thus the ranking of seismic input motions based on the tunnel response is obtained. By means of amplitude modulation, the effects of peak ground acceleration （PGA）and tunnel depth on the input motion ranking are further investigated. Finally , the correlation between different input motion parameters, including peak acceleration, peak velocity, peak displacement, absolute cumulative velocity （CAV） and Arias intensity （I_A）, and the tunnel seismic response is evaluated. Results show that, ① When PGA increases from 0.5 m/s2 to 2 m/s2, the ranking of ground motion changes apparently, and the diversity of tunnel responses caused by different input motions is significantly amplified, such that the ratio of the maximum diametrical deformation rate caused by the most unfavorable input motion to the mean value is increasing from 1.1 to 1.9; ② The input motion ranking results remain unchanged for different depths of the tunnel; ③ For the PGA of 2 m/s2, the correlation between the tunnel response and the peak bedrock velocity （PBV） matches well, i.e. the correlation coefficient is 0.94, then followed by the peak bedrock displacement （PBD） and the I_A, i.e. the correlation coefficient is 0.62 and 0.48, respectively, and the worse is, the peak bedrock acceleration （PBA） and the CAV have a correlation coefficient of only 0.37 and 0.22, respectively. The conclusions provide a scientific basis for the selection of seismic input motions of soft soil tunnels.