Steady-state and transient pressure conditions around the EPB-TBM: Numerical modelling based on experimental data

This study investigates the impact of accidental transient variations in the pressure boundary conditions applied by pressurised tunnel boring machines on the response of the surrounding soil, including that of a single pile. To this end, a three-dimensional numerical model of an earth pressure balance tunnel boring machine (EPB-TBM) was developed to simulate steady-state and transient pressure conditions. The model was carefully calibrated and validated using experimental data from the TULIP project, conducted as part of the Grand Paris Express. The study highlights the importance of careful model calibration in order to accurately reproduce the evolution of surface and subsurface settlements alongside TBM advancement under steady-state and transient conditions. In particular, the analyses demonstrate that transient pressure phases can significantly increase soil settlements and strongly impact pile behaviour, resulting in sudden displacements and the development of negative skin friction. For example, an accidental reduction in frontal pressure of around 35% during the excavation of one ring of segments can cause a rapid increase in displacement, accounting for 30%–40% of the final settlement of the pile and the surrounding soil.