Pressure Loss of Pipeline Conveying Large-Size Pebbles in Slurry Discharge System of Slurry Shield

During slurry shield tunneling in the sandy pebble stratum, the slurry discharge pipeline will transport a large number of the large irregular pebbles, generating unstable turbulence, which causes difficulties to the determination of the pipeline pressure loss. This study designed a circulating flow test device, and the slurry used in the experiment is CMC transparent viscous slurry. And the study established a numerical model using the computational fluid dynamics-discrete element method (CFD-DEM) coupling approach. Taking pebbles with a particle size of 5~80 mm as the research object, the study investigated the effects of pebble particle size distribution, slurry velocity, pebble volume fraction, and pipeline inclination angle on the pressure loss along the pipeline, respectively. The results indicate that the pressure loss along the pipeline increases exponentially with the increase of slurry velocity under the same particle size distribution, pebble volume fraction, and pipeline inclination angle. And for horizontal pipelines, the effect of pebble particle size distribution on the pressure loss along the pipeline is not significant. In addition, for the low slurry velocity (v＜2 m/s), the pressure loss along the pipeline increases linearly with the increase of pebble volume fraction. And for the high slurry velocity (v ≥ 2.0 m/s), the pressure loss along the pipeline increases exponentially with the increase of pebble volume fraction. For inclined and vertical pipelines, the pressure loss along the pipeline firstly increases slowly with the increase of the pipeline inclination angle, and then increases sharply under the same particle size distribution, pebble volume fraction and slurry velocity, and the pipeline inclination angle at the turning point is 60°. In addition, under the action of mud buoyancy and turbulence, it is difficult for large-size pebbles to overcome their own gravity and reach a state of complete suspension. Therefore, large-size pebbles mainly move along the lower wall of the pipeline, and the pressure at the elbow of the pipeline is obviously stratified.