Modified dynamic stress concentration factor for twin tunnels using a novel approach of FEM-scattering

The frequent failure of newly built tunnels under earthquake loading has led to a broader range of research into assessing the effect of seismic waves on tunnels. Numerous researchers have worked on twin tunnels and the effect of wave scattering due to vibration of harmonic waves to date. As for the near-field wave scattering and range of the recording of the acceleration of the ground during an earthquake. However, little research has been conducted on a comprehensive scale. This study attempted to examine the scattering in Si-o-seh Pol Bridge, a monument in Isfahan city, using the Hankel's function of the first and second kinds for near-field earthquakes (Northridge, Tabas and Kobe). All of scattering analysis were done through FESCAM code that designed and developed in MATLAB software as a toolbox by authors of this paper. The historic bridge of Si-o-seh Pol Bridge and its neighboring twin tunnels for subway were selected as a case study. The first kind of Hankel's function was considered as a supplementary parameter to the seismic analysis using finite element method procedure. The amount of dynamic scattering of twin tunnels subjected seismic loads considered as extra strain and stress around tunnels using Hankel's function results. The results between two cases with and without considering scattering waves of tunnels show that the mean horizontal displacement and the mean vertical displacement of Si-o-seh Pol Bridge can be increased about 28.8% and 30.11% respectively. The results of statistical analysis with Mann-Whitney test show that there is no significant difference between the seismic performance of Si-o-seh Pol Bridge with and without consideration of the scattering effect of the tunnels (P-Value = 0.6 > 0.05). However, the results of this study versus the past studies reflect the fact that horizontal and vertical displacements when involving the tunnel are 34.10% increase and −48.51% decline, respectively. This means that the twin tunnels are effective in displacement of the adjacent monument from the engineering perspective.