Practical implementation of Bi-Elliptical displacement-controlled method in analysing shallow and large tunnel excavation impact

The application of a displacement field at the excavation boundary is a widely used numerical technique for the simulation of induced displacements in the case of TBM tunnelling. Typically, a circular displacement pattern is applied, and the lining is not modelled. However, the effectiveness of this method in simulating the excavation of shallow and large shield tunnels requires further examination. In this paper, three-dimensional numerical analyses are conducted to investigate the contraction characteristics of the excavation boundary in relation to tunnel depth and diameter. Reference is made to the Tongjing Road Tunnel, China’s first large-diameter Slurry Shield tunnel under-crossing an existing high-speed railway bridge. A modified displacement-controlled method is proposed, incorporating two separate elliptical contraction shapes for the upper and lower sections of the tunnel. Its validity is confirmed by applying the method in the predicts of centrifuge tests and actual case. The numerical results indicate that for very shallow and large tunnels, the optimal deformation pattern of the tunnel boundary consists of an elliptical shape in the upper section and a circular shape in the lower section. Compared to predictions using the circular displacement-controlled method, the new approach provides more realistic estimates of the surface and subsurface displacement field. Additionally, it yields more satisfactory results in the analysis of the tunnel-bridge interaction of the examined case history.