Transport and Erosion Characteristics of Muck in the Pump–Pipeline Discharge System of Urban Shaft Boring Machines

The complex particle transport behavior and pipe wall erosion caused by long-distance solid–liquid transport in urban shaft boring machine muck discharge systems represent significant engineering challenges. In this study, a pump–pipeline solid–liquid transport model was established based on the first-stage slurry pump and vertical pipeline. A coupled computational fluid dynamics (CFD)–discrete phase model (DPM) approach was employed to investigate particle transport and erosion characteristics. The particle transport behavior at the slurry pump outlet was analyzed, and the corresponding flow field and particle parameters were transferred to the pipeline inlet to establish a transport model under practical operating conditions. The influence of particle size on particle transport behavior and erosion characteristics was further investigated. The results indicate that particle transport behavior in the pipeline is strongly influenced by the pump outlet flow field. With increasing transport distance, particle motion gradually reaches a stable transport state, and a pipeline length of 12 m (approximately 55D) is sufficient to obtain stable transport characteristics. Larger particles exhibit stronger inertia, weaker velocity response to the continuous phase, and lower axial velocity. Erosion inside the pump mainly occurs at the blade leading edge, pressure surface, and outer volute passage. During stable pipeline transport, smaller particles are more likely to migrate toward the near-wall region, causing higher wall erosion, whereas larger particles tend to remain in the pipe core region due to their stronger inertia.