Scattering Effect of Twin Tunnels on Adjacent Monuments Subjected to Far-field Earthquakes

The aim of the present study is to examine the seismic response of historical structures adjacent to twin tunnels under far-field earthquake conditions. Focusing on the Karim Khan Citadel in Shiraz and its nearby subway tunnels, numerical modeling was performed for two scenarios: with and without the presence of twin tunnels. This modeling was conducted using the Hankel function and MATLAB software (FESCAM), and through the combination of Bessel function transformation theories and numerical analyses, it enabled a precise analysis of compressional wave (P-wave) scattering in twin tunnels. This integrated approach facilitates the analysis of plane pressure waves (P-waves) in twin circular tunnels with a focus on wave scattering. The results indicated that the maximum wave scattering occurs when the incident wave angle is 30 degrees, and the tunnel orientation angle is 90 degrees. Overall findings suggest no statistically significant difference between the two case study scenarios. In addition, the horizontal and total displacement differences between scenarios with and without the tunnels were observed to range from 2.2% to 33.7% and from 2.1% to 23.7%, respectively. Therefore, the presence of twin tunnels induces changes in the horizontal stress (Sig-xx) and the principal stress (Sig-1) in the foundation of the citadel.