Seismic amplification pattern of the ground surface in presence of twin unlined circular tunnels subjected to SH-waves.

In this paper, the amplification pattern of the ground surface is presented in presence of twin unlined circular tunnels subjected to SH-waves. To analyze the assumed seismic model, a half plane time-domain Boundary Element Method (BEM) was used which has been previously developed for single sub-surface tunnels. First, after presenting a brief formulation of the proposed method and displaying a verification example, the sensitivity analysis was carried out to obtain the seismic amplification pattern of the ground surface by considering the key parameters including tunnels buried depth, interval distance, incident wave angle and response frequency. Finally, by collecting the maximum amplification of different scenarios and applying linear fit on the obtained values, the results were summarized as series of linear equations and tables. The results showed that different situations of buried twin tunnels in urban fabric was very effective on the seismic response of surface. The results of this research can be used to completing and increasing the accuracy of existing codes around the subject of ground surface zonation in presence of twin tunnels.