Optimizing the Position of Twin Tunnels for Reduction of Surface Ground Movements

In this study the deformations, ground movements, and stability of tunnels have been considered. To evaluate the effect of the position of a tunnel on surface settlement, a numerical study of twin tunnels in Shiraz City has been carried out. According to the different types of soils and the tunnel positions, the ground deformation is analyzed and discussed. Three different configurations have been taken into consideration: side-by-side, piggyback and angular-offset. Field data have been used to calculate the ground settlements caused by twin bored tunnels. A non-linear finite element analysis was performed to evaluate the surface deformations. Using the superposition approach, the empirical data have been compared with the analytical results. The results confirm that there is a clear difference in the amount and distribution of ground movements with varying tunnel positions.