Microscopic Experiments and Numerical Simulation of Foam-Conditioned Soil for Earth Pressure Balance Shield Tunneling in Water-Rich Sandy Stratum

In soil conditioning for earth pressure balance shield tunneling, foam is commonly used as an essential material to meet the requirements of tunnel excavation and soil migration. However, the interaction between foam bubbles and soil particles in the whole migration process from the soil excavation chamber to the screw conveyor is complex, which limits the further understanding of soil conditioning in water-rich stratum. This study demonstrates microscopic experiments and numerical simulation to investigate the mechanical behavior of foam-conditioned soil. The size distribution and evolution of foam were obtained through microscopic experimental observations. The contact relationships between foam–foam, foam–soil particles, and soil particles themselves were proposed. Furthermore, the Arrlinear model in Particle Flow Code software was chosen to simulate the contact relationships, and the parameters were calibrated through direct shear tests. To accurately simulate the entire soil migration process, a numerical model was established to analyze the sectional distribution patterns of foam-conditioned soil and assess the efficiency of soil discharge. Ultimately, the study provides practical construction suggestions and references based on these findings.