Numerical simulation of seepage-induced behavior of tunnel for analyzing deformation characteristic and estimating geotechnical parameters

Abstract

The Longitudinal Deformation Profile (LDP) represents the tunnel wall displacements along the axis of the tunnel, which can be used to estimate support loads and final tunnel deformations. This paper presents the effects of groundwater flow on the radial and axial LDPs of deep circular tunnels in an elasto-plastic and homogeneous ground and the usage of a back-analysis method in order to estimate geotechnical parameters using LDP under groundwater flow. A deep tunnel was chosen to remove the surface effect of shallow one, so that the analysis was concentrated on the ground response by tunnel excavation. The elasto-plastic ground was considered to sufficiently reflect how the ground behave but it may vary depending on the failure criteria and the flow rule. A number of parametric studies have been conducted, which cover a wide range of tunnel and ground conditions, liner installation, unsupported ground length and drainage conditions at the tunnel wall (fully drained and partially drained cases). The seepage forces are developed in the fully drained case, resulting in the increase of effective stresses in the radial and axial directions. The pore pressure developed in the partially drained case squeezes the tunnel wall radially, not axially. The liner installation and the unsupported ground length also affect tunnel wall deformations. Results from the numerical simulations show that the groundwater flow at the tunnel wall influences deformations both radially and axially. For the application of these results, a back-analysis which uses a relative convergence curve determined from LDP is performed to estimate geotechnical properties. Several numerical studies have been conducted in order to test this back-analysis method. The results show that estimated parameters match well with the real parameters.