Arash Tunnel is an 1870 m underground urban tunnel project, which is under construction, in Tehran by New Austrian Tunneling Method (NATM). Due to the existence of different entrances and exits in its traffic scheme, it comprises various traffic lane sections like one-lane, two-lane, three-lane, twin two-lane and two-story two-lane sections. In this paper, we are going to declare our experiences during the design and the construction of the most complex part of this project, a twin tunnel. Valiasr tunnel is composed of two connected initial and two discrete adjacent final lining tubes. Based on a comparison between the monitoring data and the numerical simulation results, the contractor is requested to use additional supports or alter construction sequences for the sake of risk reduction. Relevant information concerning primary and subsequent designs, monitoring data, as well as numerical modelling procedures and results will be explained in this paper.