External hydraulic pressure and invert uplift study in a non-circular shallow tunnel

Water hazards experienced in mountain tunnels have always been associated with inadequacy of waterproof structures and grouting technology applied in the construction stage. But the knowledge of seepage caused by groundwater inflow during the operation stage remains limited despite its importance to tunnel traffic operation and general safety. In this paper, the concept of equivalent permeability lining is introduced and the external hydraulic pressure (EHP) distribution of shallow non-circular tunnel is analytically deduced. A set of numerical and model tests are presented based on the semi-enclosed drained tunnel of a high-speed railway in China. The result shows that the existing circular solution underestimates the invert external hydraulic pressure (EHP) of non-circular shallow tunnel. A staged failure mode of high-EHP semi-enclosed tunnel can be observed in model tests. The vulnerabilities of warning criterion and monitoring put the high EHP tunnel under risk. Based on these, a modified analytical solution, a new warning criterion and a new maintainable monitoring system are built for high EHP tunnel.