A function fitting method for tunnel convergence evaluation

In urban regions, tunnel construction has gained popularity due to its ability to expand available urban space. Tunnel periphery deformation can affect the integrity of tunnel structure and the stability of adjacent constructions. Existing tunnel convergence fitting methods, such as circle and ellipse fitting, are limited by their idealised shapes and inability to integrate with displacement-controlled method for numerical simulations. To address these challenges, this study proposes a function fitting method to systematically describe tunnel convergence characteristics using field-measured data, with the tunnel central angle as an independent variable. Through applying the fitted functions as displacement boundary conditions in finite-element simulations, the short-term effects of tunnel convergence on the surrounding environment, such as ground subsidence, stress distribution, and axial force and bending moment within the liner, can be quickly assessed. The effectiveness of the proposed method is verified by case studies. Results indicate that this method can describe tunnel convergence effectively and evaluate tunnelling-induced ground surface settlement (GSS) efficiently. In addition, at the early phase of tunnelling, where the tunnelling data are limited, the gap parameter and volume loss can be utilised to provide a probability analysis of GSS trough.