Discovering the optimal distance between spatial orthogonal tunnels: A dynamic analysis using Tehran metro as a case study

This study investigates the dynamic behavior of spatially orthogonal tunnels by employing three-dimensional numerical modeling and analyzing four different placement scenarios to determine the optimal tunnel spacing for minimizing mutual interaction while ensuring operational efficiency. This comprehensive research fills a vital gap in dynamic tunnel interaction studies and provides valuable insights for tunnel engineering in urban environments. Furthermore, in this research, the influence and response of adjacent shield tunnels under seismic conditions was evaluated based on the Tabas earthquake spectrum. Moreover, to enhance the accuracy of assumptions and achieve more logical results, the study utilizes the assumptions of the intersection tunnels of lines 6 and 7 of the Tehran metro. Dynamic analyses reveal that closer tunnel proximity (<0.5r) leads to increased bending moments, axial forces and displacements due to stress field interference, underscoring the critical importance of proper tunnel placement. Furthermore, results of the internal forces and displacements in both adjacent tunnels under dynamic loading show that positioning scenario case 2 (distance of tunnels is equal to their radius) is the most suitable option. In this scenario (compared to scenario case 1), the tunnels are less affected by each other’s stress field, and also in this positioning scenario (compared to scenarios 3 and 4), access from the ground surface to the lower tunnel will be easier and with lower construction costs.