Influence of cutterhead opening distribution on muck migration and excavation characteristics during slurry shield tunneling: an FDM-DEM-CFD coupling analysis

Cutterhead opening parameters are important for slurry shield TBM design, yet existing studies mainly focus on opening ratio while neglecting the influence of opening distribution. Taking the 16.6 m diameter slurry shield TBM in Haitai Yangtze River Tunnel project as an example, the present study established an integrated FDM-DEM-CFD coupling model to investigate the effects of cutterhead opening distribution and ratio on muck migration and excavation characteristics. A cutterhead opening distribution coefficient K u is proposed as the ratio of the central opening ratio to the peripheral opening ratio, and simulation schemes are designed covering three opening distribution coefficients ( K u = 0.5, 1.0, 1.5) and three opening ratios ( α = 35%, 45%, 55%). In addition, the muck retention time is proposed as an explicit indicator for visualizing the spatial distribution of muck retention within the excavation chamber. The results indicate that muck preferentially enters the excavation chamber through the peripheral opening region. A smaller K u increases the tendency of muck accumulation in front of the cutterhead center, thereby weakening particle mobility and increasing the risk of mud cake clogging. Particles with prolonged retention time are predominantly concentrated adjacent to both sides of the slurry discharge gate. More particles with shorter retention times are discharged from the excavation chamber under K u = 1 compared to K u = 1.5 and 0.5. Under a fixed opening ratio, a lower K u increases the stress applied on the central face but decreases the stress at the lower edge. The rotation of the cutterhead creates asymmetric muck accumulation in the excavation chamber, which in turn causes asymmetric stress distribution at the lower edge of the tunnel face. In the 45%-55% opening ratio range, a cutterhead with K u ≈ 1.0 achieves a balanced trade-off among thrust, torque, and uniform muck entry, with comparable muck inflow per unit area between the central and peripheral opening regions. At a 35% opening ratio, a maximized central opening ratio is suggested to avoid excessive thrust and torque. These findings provide practical insights into cutterhead design, clogging control, and parameter optimization for large-diameter slurry shields in soft soil strata.