Investigation on optimal soil chamber pressure settings for EPB shield machines in sandy cobble strata with insights from gravel flow characteristics

In sandy cobble strata, setting the soil chamber pressure in Earth Pressure Balance (EPB) shields is crucial for ensuring construction safety. Traditionally, pressure values are determined empirically, often leading to inefficient tunneling or instability of the excavation face. This study, based on a Chengdu Metro project, employs discrete element modeling and theoretical analysis to investigate appropriate soil chamber pressure settings. A three-dimensional model representing the interaction between the stratum and the cutter head was developed, enabling the analysis of gravel flow characteristics within the chamber. The analysis identified a critical lower limit for chamber pressure—0.6 times the earth pressure at rest—necessary for stabilizing the excavation face. Furthermore, muck movement within the chamber was theoretically analyzed using a cylindrical laminar flow model. Based on these analyses, an approach for optimal soil chamber pressure setting was derived. This approach ensures that the earth pressure at the tunneling face is balanced with the earth pressure at rest, providing a theoretical foundation for minimizing the environmental impact of shield tunneling operations. The proposed method was validated through field cases in sandy cobble strata, offering valuable guidance for similar shield tunnel projects.