Numerical Assesment of Support and Reinforcing Techniques of Alborz Tunnel

Despite the development of numerous excavation methods and reinforcement of tunnels, finding a proper method for stabilization of underground structures is a challenging task. The use of pre-reinforcement systems is an appropriate method to improve the status of the ground. In this study, the performance of umbrella system in Alborz tunnel in north of Iran has been investigated. Rock mechanics studies of tunnel running area have shown that parts of this tunnel have unstable capacity due to being located in weak zones. Therefore, the tunneling operation running is not possible in these areas. On this basis, umbrella pre-reinforcement system that can be used for loose and running ground are modeled numerically by Flac3D software. In this research, in addition to investigating the performance of umbrella system, the effect of geometrical parameters such as the angle of placement of pipes relative to the horizon and the distance between the umbrella system pipes was investigated. The criterion of investigating is the displacement occurred at the crown of the tunnel. The results of this study indicate that increasing the angle and decreasing the distance between pipes, cause an increase in stability and by using umbrella system, the vertical displacement of crown of the tunnel has decreased by 70 %.