Effect of surcharge loading on horseshoe-shaped tunnels excavated in saturated soft rocks

Abstract Underground facilities are usually constructed under existing buildings, or buildings are constructed over existing underground structures. It is then imperative to account for the current overburden loads and future surface loadings in the design of tunnels. In addition, tunnels are often constructed beneath the groundwater level, such as cross-river tunnels. Therefore, it is also important to consider the water pressure impact on the tunnel lining behaviour. Tunnels excavated by a conventional tunnelling method are considered in this paper. The hyperstatic reaction method (HRM) is adopted in this study to investigate the effect of surcharge loading on a horseshoe-shaped tunnel behaviour excavated in saturated soft rocks. The results obtained from the HRM and numerical modelling are in good agreement. Parametric studies were then performed to show the effects of the water pressure, surcharge loading value and its width, and groundwater level on the behaviour of the horseshoe-shaped tunnel lining, in terms of internal forces and displacements. It displays that the bending moment, normal forces and radial displacements are more sensitive to the water pressure, surcharge loading and groundwater level.