Probabilistic Face-Pressure Windows for EPB Tunnelling Under Dynamic Excavation

ABSTRACT: Face stability in Earth Pressure Balance (EPB) tunnelling is commonly assessed using static and deterministic approaches that neglect dynamic cutterhead rotation, cutterhead opening ratio, and soil spatial variability, and typically focus only on collapse. This study presents a three-dimensional coupled Eulerian–Lagrangian (CEL) large-deformation modelling that explicitly incorporates dynamic cutterhead rotation and opening ratio, enabling simulation of soil cutting, chamber pressure, face collapse, and blowout within a unified framework. The deterministic model is extended to probabilistic analysis using random field modelling of undrained shear strength and Monte Carlo simulations. Results quantify chamber pressure thresholds for both collapse and blowout and demonstrate their sensitivity to cutterhead opening ratio in both uniform and spatially variable soils. For opening ratios of 30% and above, neglecting cutterhead rotation and opening effects can lead to unsafe face pressure design. Moreover, soil spatial variability increases dispersion in critical pressures and raises the likelihood of premature collapse and blowout. These findings highlight the importance of accounting for dynamic cutterhead effects and soil heterogeneity when defining safe face pressures in EPB tunnelling.