Discharge behavior of spherical and rock chip mucks by screw conveyors in TBM: Physical model experiments and DEM simulations

Abstract

The discharge of muck through a screw conveyor system plays a crucial role in ensuring safe and cost-effective tunneling with earth pressure balance tunnel boring machines (EPB-TBM). However, the discharge mechanism of chip-type rocky mucks through a screw conveyor has not been well examined. Therefore, this study investigates the discharge behavior of rock chips through a screw conveyor by using a 3D discrete element model (DEM). Numerical simulations are conducted with rock chip particles of various sizes, as well as spherical particles, while varying the inclination angle, screw pitch length, and rotational speed of the screw conveyor. The simulation results show that the relative size between the muck particles and pitch has a significant effect on the discharge rate, and an optimal ratio of pitch to flight diameter is suggested. The particle-level analysis reveals distinctive particle discharge paths and a velocity distribution of muck particles along the screw axis. The study proposes the ratio of the screw pitch to the maximum particle size as the primary design parameter to predict the discharge rate. This is because large particles play a critical role in determining the discharge rate. The study highlights the usefulness of 3D DEM-based simulation as a tool to investigate discharge behavior of particulate materials through a screw conveyor. Moreover, it advances our understanding of rock chip-type muck discharge behavior during TBM excavation, providing guidance for screw conveyor design and feedback during TBM operation.