Operational challenges of the first ever Double-arch road tunnel in Iran

Choosing the type of a tunnel and construction technique depends on several factors in the project. Environmental, social, and geological concerns and the like create several challenges and overcoming them entails adequate studies and accurate planning throughout feasibility, design, and construction phases. Tunnel No.6 of Tehran-North Freeway, as the most special road tunnel in Iran, was the first ever double-arch tunnel implemented by a team of Iranian experts. The operation faced with all the challenges mentioned. Numerous operational stages, construction of pilot tunnel, implementation of middle wall, finding a way to connect the wall to the two side tunnels, designing the connections, digging side tunnels at multiple stages given the condition and type of ground (progress using side pilot tunnel in unstable grounds and complete-face digging operation afterward), immediate consolidation after each digging step (using lattice, mesh, shotcrete, rock bolt, fore poling), bottom lining, final lining, and sealing methods all were carried out in more than one active site to meet the deadline of client. Handling all these needed a comprehensive and accurate management. The present paper explains the achievements of the tunnel contractor, the challenges, and the way that we overcame them, which will hopefully be useful for future similar operations in Iran.

Keywords:

Tehran North Freeway , Double-arch tunnel , pilot tunnel , side pilot tunnel