Three dimensional modeling and design of Tohid highway urban tunnel based on the analysis of controlled underground deformation and settlement

Tohid Highway urban tunnel at Tehran city comprises twin 12m diameter tunnels constructed by NATM method at shallow depth under crowded Navab-Chamran highway. Construction shallow large section tunnels should be considered as stability and reducing ground settlement point of view. Three dimensional numeric analyses using the finite difference program FLAC ^3D carried out in order to detect important parameters for designing and monitoring behavior of tunnel. This paper describes designing conventional tunneling techniques and improvement support system using the approach based on the analysis of controlled critical strain and settlement. Method of constructing in an optimum excavation pattern has been considered to induce stresses to lower level of ground by piles. Support system comprised with lattice and shotcrete and also central and lateral piles numerically designed by considering rate of advancement and its affect on tunnel and superficial displacement. This procedure results in avoiding any time consuming solutions like Pre-Supporting System and provides a restraining effect on the tunnel induced displacement.