Influence of Embankment Loading on the Hydro-Mechanical Response of a NATM Tunnel in Saturated Ground

摘要

Tunnel design in urban areas must account for overburden loads as well as additional loads imposed by future surface infrastructures, called the embankment load. In saturated ground, the embankment load will generate not only mechanical response through stress and displacement changes, but also hydraulic response through pore pressure changes. Because this hydro-mechanical (H-M) response will be transferred to the tunnel liner and because the liner deforms with the ground, the embankment load will correspondingly influence the liner's stability. This paper examines how severely the induced H-M response from the embankment load will affect the integrity of a horseshoe-shaped (NATM) tunnel in saturated ground. Two tunnel models are created in the computer code FLAC. One model is under weak and low-permeability ground (i.e., clay), and the other one is under relatively strong and high-permeability ground (i.e., granite). Each tunnel model is run under different liner drainage conditions: permeable and impermeable. The embankment load is then applied 10 years after tunnel construction. Simulation results suggest that impermeable tunnels will experience the most severe bending moment from the embankment load, particularly for tunnels in clay. Further, the severity does not stop shortly after the load is applied, but continues towards the steady-state.