Investigation of Jamming Possibility of Tunnel Boring Machine (TBM) – A Case Study: Qom Metro Project

The phenomenon of TBM jamming is one of the most hazards in full mechanized tunneling projects that should be considered at design time. This paper investigates the jamming possibility around full face excavation machine in Qom metro project. To achieve this purpose, different solution methods including empirical relations, analytical solutions and numerical modeling have been used. Since the excavation environment is continuous, to analyze the tunnel based on the numerical method, the Plaxis 3D software is used. Based on the results, in some areas, there are face instability and also the possibility of TBM jamming. It should be mentioned that the obtained results are function of the analysis method so that the calculated support pressure in numerical modellings is larger than its value in the other methods. Tunneling in weak and low resistance environments presents significant design challenges. As the resistance parameters of these media are low, the displacement analysis and the assessment of the non-elastic zone characteristics are very important, especially in areas where there are numerous high-rise buildings. Furthermore, the tunneling-induced ground displacement has a great influence on existing urban structures, and the evaluation of displacements (in the design stage) is a difficult subject, which many tunneling engineers have encountered. In these media, tunneling by TBM is an effective method to control the ground displacements. However, when a large time dependent deformation occurs around the tunnel, the ground pressure imposed on TBM shield could cause TBM jamming. Therefore, the jamming prediction in full mechanized tunneling projects is an essential part of tunnel design and machine selection. The Qom metro project is one of important urban tunneling projects in Iran. In this project, about 10 kilometers of the entire tunnel are excavated by an earth pressure balance (EPB) shield TBM. The main purpose of this paper is to investigate the jamming possibility surrounding shield of EPB-TBM in the Qom metro project. The pressure required for the face stability was calculated using empirical, analytical and numerical methods. The numerical modeling in this study is carried out using Plaxis 3D software. Moreover, a comparison is made between the results of different methods. Finally, the effect of various parameters on the face stability and jamming possibility is evaluated via sensitivity analysis carried out in this research work. According to the results, when the ratio of overburden to tunnel diameter is more than 2, the results of the analytical and numerical methods are similar. The differences in results are due to differences in the parameters and the behavioral model used in the numerical modeling and analytical methods. For example, in some analytical methods, for excavation medium, the elastic behavior is considered, while in three-dimensional (3D) numerical modeling, several non-elastic behaviors could be considered.