A calculation method for the ultimate support pressure of a shield tunnel excavation face accounting for fault dip angle

Abstract This study investigated the influence of fault dip angle on tunnel excavation-face stability. Starting from the conventional wedge instability model for homogeneous strata, an associated flow rule was introduced to improve the wedge model, and a modified wedge calculation model that accounts for the fault dip angle is proposed. Then, by establishing the compatibility relationship between the rupture angles of the upper and lower strata, an analytical formula for the ultimate support pressure of the excavation face under inclined fault conditions is derived using the limit equilibrium method, along with the corresponding calculation procedure. Three-dimensional numerical simulations are performed to evaluate the theoretical model, and the results reveal that the trends in the theoretical predictions and numerical simulations are consistent, with relative errors ranging from 3.2% to 15% across all working conditions, indicating good agreement between the theoretical and numerical results. The calculation results reveal that stratum strength parameters and fault dip angle are the key factors controlling ultimate support pressure. The proposed calculation method for the ultimate support force of the excavation face considering fault dip angle can quantitatively estimate ultimate support pressure in faulted strata, providing a theoretical basis for assessing support parameters and evaluating excavation-face stability during slurry-shield tunneling through fault fracture zones.