A 3D numerical model to determine suitable reinforcement strategies for passing TBM through a fault zone, a case study: Safaroud water transmission tunnel, Iran

Abstract

Abstract Mechanized tunneling, like other tunneling methods, is not an exception to dealing with complex geological structures in its direction. Therefore, the accurate perception of the geological structures and anomalous through the tunnel path and the challenges ahead of TBM can minimize the operational risk. The faults are complicated, loose, seismic, and saturated structures that present a great deal of danger when passing the tunnel from them, and each of these events, in turn, has the potential to stop the project and exert high economic costs. The instability of the tunnel environments and tunnel face due to the higher amount of stress concentration than the resistance of the host rock, pulpy material flowing from inside of the faults and water inrush are the most important events that TBM faced them through the fault zones. Hence, using the appropriate tool for realizing the operational model can be a considerable help in predicting problems. In this research, using precision numerical methods, accurate simulation of TBM motion was carried out to the excavation of Water Transmission Tunnel, Iran. The Safaroud water transmission tunnel is one of the longest Iranian water transmission tunnels that passes through numerous fault zones along its path. One of the main faults in this area is the Lalehzar fault with 40\u202fm width which motivates us to utilize predicting procedure. The main purpose of this research is numerical modeling of mechanized tunneling in fault zone using FLAC3D and Phase2 software and selection of suitable reinforcement strategies for passing TBM from the fault zone. The results of numerical modeling illustrate the instability of the tunnel in the Lalehzar fault zone. Due to tunnel instability in this zone, reinforcement operations must be taken into account to stabilize the tunnel environment. The numerical modeling of the several reinforcement operations in the fault zone were simulated and we conclude that the combination of umbrella arch and radial grouting method are the most suitable strategies for passing TBM from the Lalehzar fault zone.