Finite Element Analysis for Parametric Study of Mega Tunnels

Abstract

The development of any country has a positive relation to the infrastructural development, and the tunnels are a very much important part of it. The increased need for tunnel infrastructure in urban areas demands tunnel excavation using Tunnel Boring Machine (TBM) to avoid surface traffic disturbance during the project execution period. The construction of Mega Tunnels provides a successful and profitable solution for urban development. Mega Tunnel is a large-diameter tunnel in which the diameter is greater than 10 m. The construction of Mega Tunnels involves more cost of construction for the station, as we must go deeper for stability purposes. Face Stability of such types of tunnels has been a hot topic for researchers, as this issue gets more critical with the increase in tunnel diameter. The collapse pressure plays an important role in the face stability of tunnels with increased overburden. Therefore, with the advantage of mega tunnel construction, ground-induced settlement and deformation should be taken into account. This paper focuses on the ground-induced settlement at various cover to diameter (C/D) ratios. The parametric study had been done by three-dimensional finite element analysis using Midas Gtx Nx software with different C/D ratios and pressure parameters for soft soil. The diameter of the tunnel is considered as 15 m. The analysis showed that the application of requisite pressures plays a significant role in the face stability of mega tunnels. Conclusions were drawn based upon analysis, and approximate preliminary lining thickness was suggested for different C/D ratios, which will be beneficial to ascertain preliminary tunnel design in actual practice.