Analysis of flow field characteristics and factors influencing the excavation chamber in large-diameter slurry shield

The study aims to improve the flow field characteristics in the excavation chamber of the slurry shield to mitigate cutterhead clogging under cohesive strata. The Computational Fluid Dynamics (CFD) method is employed to quantitatively investigate the impact of scouring flux, cutterhead rotational speed, adding nozzles, and excavation methods on the flow field characteristics. Results show that increasing the existing scouring system flux even to 2000 m3/h couldn’t improve the slurry flowability at the cutterhead periphery. However, increasing the cutterhead rotational speed can significantly improve the slurry flowability at the cutterhead periphery and opening, resulting in a more uniform distribution of the flow field. Similarly, adding nozzles at the cutterhead periphery has positive effects. When the total scouring flux of 6 additional nozzles reached 800 m3/h, a favorable scour effect is achieved near the excavating face. Furthermore, adopting the air pressure assisted mode, the flowability of slurry at the cutterhead opening shows a significant enhancement compared to the full-chamber, and upper-half nozzles are transformed into non-submerged jets achieving a better scouring effect. Based on the analysis, it is recommended to add nozzles at the cutterhead periphery. If geological conditions permit, the “high-speed, low-penetration” or air pressure assisted excavation mode can be attempted.