Discharge behavior of spherical muck mixed with acrylamide polymer solution by screw conveyors in TBM tunnelling

A screw conveyor is worn down while it discharges muck during TBM excavation. In order to prevent downtime caused by screw conveyor damage, polymer is injected into the TBM chamber to achieve uniform mixing with the muck, after which the polymer and muck mixture is discharged through the screw conveyor. Thus, this paper investigates the impact of polymer on the discharge rate of glass beads instead of real muck, by a screw conveyor through scaled-down screw conveyor experiments with different polymer concentrations while different rotational speeds of the screw conveyor. There is a clear tendency for the discharge rate to decrease until the polymer concentration reaches 0.5 %. However, beyond a polymer concentration of 0.5 %, the degree of decrease in the discharge rate as the polymer concentration increases is minimal. The particles coated with polymer are discharged by moving in a spiral pattern along the screw flight by the cohesion of particle-to-particle, and particle-to-screw flight in the screw conveyor. Additionally, the numerical analysis using the discrete element method (DEM) confirms that the polymer's cohesion causes the particles to move more slowly within the chamber. These findings provide valuable insights for TBM operations, specifically regarding the discharge rate of muck when employing polymers.