Development and Application of the Bi-Elliptical Displacement-Controlled Method for Improving TBM Tunnelling Simulations

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 without moddelling the lining. However, the effectiveness of this method in simulating the excavation of shallow and large shield tunnels requires further examination. This paper introduces the Bi-Elliptical Displacement-Controlled Method (DCM) for extending the application scope of the Circular DCM and enhancing the accuracy and applicability of DCMs, particularly for shallow large-diameter tunnels. This method, developed on the basis of theoretical assumptions and verified by three-dimensional finite element analyses, assumes a new displacement pattern characterized by independent elliptical contractions for the upper and lower sections of the tunnel, while also accounting for its overall vertical translation. The deformed tunnel profile is controlled by three deformation parameters, functions of the tunnel geometry, excavation conditions, and soil properties. Two Python-based automation tools for Plaxis 3D were developed and described in detail to aid in the calibration of deformation parameters and efficient application of the method. The method and tools were validated through their applications to back-analyse a large and shallow tunnel excavation both in free-field conditions and below a high-speed railway bridge. This approach holds considerable potential for applications in information-based construction and real-time Design-Build processes.