Variations in Ground Surface Responses Under Different Seismic Input Motions Due the Presence of a Tunnel

This paper examines the interaction between urban tunnel and ground surface during the different input motions. The Niyayesh-Sadr tunnel in North of Tehran with a 14m span and its environmental conditions were used as a case study. Analysis is performed using a finite difference model which takes into consideration the presence of the tunnel during the seismic motion. The soil behaviour is assumed to behave according to the Mohr-Coulomb model, and hysteretic damping is included in the dynamic analyses. Previous studies showed high amplification of displacement in the vicinity of the tunnel. This paper comprises three parts wherein the effects of the presence of a tunnel on surface accelerations, which are the basic input data used in the design of buildings, are investigated. The first part illustrates the numerical method with the related verifications. In the second part, two parameters of acceleration amplification factor and acceleration interaction factor are described. These parameters are calculated during several Ricker wavelets with different predominant frequencies and selected earthquakes with various frequency contents. The last part examines the variation of the shear strains near the surface and the residual strains. Results show that the presence of tunnel can increase the surface acceleration up to 37 % in critical cases. The distance between 0.5D to 1.0D from the centre of the tunnel on the surface is mostly affected by considering the interaction so that in the present case study, most of the buildings are placed in this critical zone.