Complex variable analytical prediction for ground deformation and lining responses due to shield tunneling considering groundwater level variation in clays

Shield-driven tunneling will encounter huge risk of potential accidents as a consequence of groundwater level surprising variation in the course of construction. Current studies seldom take account of the groundwater level variation during construction for tunneling-induced ground and tunnel responses. Moreover, little work is conducted on the analysis of tunnel lining deformation and stress. For better tunnel serviceability and safety, this paper presents a closed-form analytical solution for predicting the tunneling-induced responses of ground and tunnel lining in clays considering the influence of groundwater level variation. By introducing the non-uniform convergence deformation pattern, along with the conformal mapping, the authors establish sufficiently appropriate boundary conditions for the complex soil properties of different mediums in the problem and the corresponding complex variable solutions are derived. The accuracy of the presented solutions is then verified by comparisons with the numerical solution, showing reasonable alignments. It can also be concluded form the comparisons that the effective stress of soil weight above the tunnel receives a notable increase on the condition of a groundwater drawdown, which inevitably generates ground movements and adversely affects the tunnel safety. Furthermore, parametric analyses are also performed for the influence of concerned parameters on the lining responses, namely, lining thickness, tunnel radius and groundwater level, in which the distribution of lining stress and deformation is described in details. In general, the closed-form analytical approach introduced in this literature provides an effective insight into the soil-lining interaction involving groundwater level variation as a potential risk, which can serve as an alternative approach for conservatively estimating ground and tunnel responses in the preliminary design of tunnels.