Numerical analysis of inclined-tunneling effect on the stability of main tunnels of Tehran-Shomal (North) highway

Tehran Shomal highway passes through Alborz mountains with a tunnel length of 6400 meters. There are two main tunnels. A full three-dimensional (3D) numerical analysis coupled with elasto-plastic material models was conducted on the inclined access tunnel. Bending moment, axial force and the lining displacements due to the internal forces applied on the shotcrete lining are calculated. Axial force and bending moment applied on the lining have been evaluated using the FLAC 3D software program. The axial force versus bending moment of the lining is plotted. A criterion for assessing the effect of intersection on main tunnel behavior has been established, and investigated stability main tunnels by excavation of inclined access tunnel and a new support system suggested because of high-stress concentration at the junction. Raising support axial forces and bending moments may endanger tunnel stability during construction in the intersection of the inclined access and main tunnels. The results indicate that the existing thickness of the tunnel lining is safe and provides the appropriate load and moment bearing capacity.