Effect of tunnel depth on the ampliﬁcation pattern of environmental vibrations considering the seismic interaction between the tunnel and the surrounding soil
The amplitude and frequency of seismic waves caused by earthquakes change as they propagate in the subsurface environment. This change is further influenced by the presence of underground structures and the kinematic interaction between the structure and the propagating seismic wave. Analysis of ground motion and subsurface propagation of a seismic wave in the presence of an underground structure needs to include appropriate ground input motion parameters. Thus, to ensure security of important engineering structures and to prevent environmental damage under earthquake excitation the dynamic response of the vibrating underground structure and subsurface wave propagation interaction problem needs to be analyzed carefully. The aim of this study is to evaluate the results of the amplification effect on free field motions and the underground structure considering the tunnel-soil structure using numerical tools. The 2-D finite element method was used as a numerical model to determine the magnification effect of seismic excitation with various frequencies on surface vibration in the presence of a tunnel structure. The analysis includes various local soil conditions with different shear wave velocity were considered to evaluate the seismic behavior of the vibrating tunnel-soil system and its environmental impact. To evaluate the change in amplification patterns, the analysis was first performed on the free field and then the results were compared with the case where a tunnel structure was present. Then, the similar influences were investigated by using the numerical tool considering other parameters such as tunnel depths and soil characteristics. Results indicate that the presence of underground structure amplified the seismic vibrations on the free field and tunnel depending on the frequency of the external load and the local soil condition.