Non-linear dynamic analysis of the lined tunnel effect on the surface amplification considering tunnel-soil interaction

In this study, effect of a tunnel as an underground irregularity on the dynamic response of the surface is investigated. To attain this goal, the variation of the frequency content and amplification behavior of the surface because of the presence of the tunnel is estimated by a time domain fully nonlinear analysis method. To make the results useful in practice, the variation of the maximum spectral amplification factor (MSAF) as the average of the site response to twenty-four real earthquakes scaled to a target spectrum are estimated for two soft and stiff clayey sites with tunnels at two different depths. The results showed that while the maximum response spectrum of the surface points close to the tunnel axis happens in lower period, it moves to the higher period by the increase distance from the tunnel axis. It was seen that the main reason of the seen amplifications is the change in the frequency content of the surface points. Also, the affected surface distance from the tunnel axis is greater for the soft clayey site case. By the increase in the tunnel depth, the location of the MSAF peak point moves farther from tunnel axis. Also, the increase in the tunnel depth decreases the MSAF. Considering the dimension and geometry of the cases studied in this study, no sign of the surface wave generation due to the presence of the tunnel was encountered.