Elastoplastic Analysis of Circular Tunnel in Saturated Ground Under Different Load Conditions

When a tunnel is excavated below the groundwater table, groundwater flows in through the excavated wall of the tunnel and seepage forces act on it. These forces significantly affect the ground reaction curve, which is defined as the relationship between the internal pressure and radial displacement of the tunnel wall. This study investigates analytical solutions for seepage forces acting on the lining of a circular tunnel under steady-state groundwater flow. Considering the tunnel’s construction or service period and boundary conditions, the direction of maximum principal stress changes, and the input stress of the Mohr-Coulomb criterion varies. The stress distribution and yield range of the surrounding soils and linings are studied. The first, second, and third critical inner pressures are defined and evaluated. The influence of the seepage field on the plastic radius, first critical pressure, and stress distribution of the tunnel is analyzed. It is shown that during the construction period, the seepage force promotes the expansion of the yield area, whereas during the service period, the opposite is the case. The first critical pressure increases nearly linearly with the distant water pressure. The radial stress distribution decreases clearly in comparison with that when the seepage force is not considered, and the reduction is more prominent when internal pressure increases. The tangential stress distribution increases clearly compared with that when the seepage force is not considered.