Numerical study on the muck flow behavior in the screw conveyor during EPB shield tunneling

The muck flow behavior in the screw conveyor determines the pressure in the excavation chamber. The pressure in the chamber should be reduced to the atmospheric pressure at the outlet of the screw conveyor. Otherwise, the soil and water mixture would spew out form the screw conveyor, resulting in the pressure loss and face failure. In this study, three-dimensional numerical analyses of the muck transport performance of screw conveyor were performed using Computational Fluid Dynamics (CFD). The muck was assumed to behave as a Herschel-Bulkley (H-B) plastic fluid. A new model coupling rheological and wall slip models was developed and validated by a laboratory test. The error of the pressure transfer and the flow rate between simulation and test is around 3.8%. Through parametric analysis, the influence of the rheological parameters of muck and the working parameters of the screw conveyor on the muck flow behavior is further explored, and a spewing failure surface is given for the control of rheological parameters of the conditioned soil. The results in this study could provide some suggestions for soil conditioning and the optimization of screw conveyor performance.