The Effects of Tunnel Excavation on the Seismic Response of Ground Surface Using Finite Difference Method

Increasing urban populations and creating traffic problems, the use of the underground spaces in the transportation is inevitable. Recent studies have shown that seismic response of ground on tunnels can differ from free field movement during earthquake and change the model of propagation of seismic waves. However, these effects have not been used in the seismic standards for the design of surface structures. In this research, using the finite difference method and FLAC 2D software, the effects of tunneling on earthquake amplification on the surface has been studied. For this purpose, the variation of the shear wave velocity of the soil under harmonic waves by different frequencies and amplitudes in both forms of the presence of a tunnel and in the free field have been investigated. The results of the studies showed that soil hardness and frequency of waves have a significant effect on the site response, and can increase the acceleration of the surface in harmonic waves to about 1.3 and with the acceleration of the Bam earthquake to about 1.7 times. Whereas, the presence of tunnel does not affect at longer distances of 15 times its radius. The coefficients obtained the site response can be used in seismic zoning of urban areas and for the design of seismic structures in the area affected by the tunnel.