Modified Dynamic Stress Concentration Factor for the Scattering of P-wave by Twin Tunnels

Stress concentration around twin tunnels and its impact on monuments have been receiving much attention from researchers. To investigate the effect of scattering in twin tunnels, the Hankel function of the first kind has been used by various researchers. The mathematical relation of Fourier expansion was modified and the time-domain analysis was transformed to frequency-domain analysis to provide a novel method for analyzing stress concentration factors. The combined finite element scattering model (FESCAM) was designed and developed in MATLAB. Analysis was performed in the presence of twin tunnels with a scattering of P-wave and in the absence of twin tunnels under the effect of a near-field earthquake. According to the results, dynamic stress concentration factor (DSCF) for Kobe earthquake P- wave with different wave angles and maximum frequency showed maximum scattering at α=0° and θ=0° in the tunnel. In addition to the increased stress concentration factor, the results of the Mann-Whitney statistical test in SPSS revealed a significant difference between the seismic performance of Arg-e Karim Khani and Zand underpass in the presence and absence of the tunnel (P Value 0.05). A scattering effect of less than 10% was calculated taking into account the combined effect of the calculated seismic waves using incremental extended finite element software. Scattering depends on frequency, and higher scattering was reported for higher frequencies.