The ground reaction curve due to tunnelling under drainage condition

When a tunnel is excavated below the groundwater table, water flows into the excavated wall of tunnel and seepage forces are acting on the tunnel wall. Such seepage forces significantly affect the ground behavior. The ground response to tunnelling is understood theoretically by the convergence- confinement method, which consists of three elements: longitudinal deformation profile, ground reaction curve, and support characteristic curve. The seepage forces are likely to have a strong influence on the ground reaction curve which is defined as the relationship between internal pressure and radial displacement of the tunnel wall. In this paper, seepage forces arising from the ground water flow into a tunnel were estimated quantitatively. Magnitude of seepage forces was determined based on hydraulic gradient distribution around tunnel. To estimate seepage forces, different cover depths and groundwater table levels were considered. Using these results, the theoretical solutions for the ground reaction curve (GRC) with consideration of seepage forces under steady-state flow were derived. Copyright ASCE 2008.