Investigation into the flow characteristics of slurry shield pipeline system under sandy pebble stratum: Model test and CFD-DEM simulation

Due to the increase of large irregular pebbles in the pipeline system during slurry shield tunneling in sandy pebble stratum, the transportation of the muck is particularly complicated. In this study, a pipeline test system was designed and a three-dimensional transient slurry-pebble numerical model was established based on computational fluid dynamics-discrete element method (CFD-DEM) coupling method to grasp the flow characteristics of slurry shield pipeline system, which involves three aspects: the pebbles critical velocity, the pipe pressure drop and the pebbles movement trajectory. In the model test, the CMC slurry was assumed as the carrying liquid and the hypothesis was verified. In the validated CFD-DEM coupling model, the rheology of slurry and the shape of large irregular pebble were considered via rheological tests and 3D scanning technology respectively. The results indicate that, firstly the critical velocity of pebble increases and then decreases with the increase of equal volume particle size under the same shape of pebbles and pipe inclined angle, and the critical velocity of ellipsoidal pebbles is greater than flattened than subspherical for the different shape pebbles under the same particle size and pipe inclined angle; Secondly, for horizontal straight pipe, the pressure drop increases exponentially with the increase of slurry velocity, and the effect of the particle gradation of the pebbles on the pressure drop in the pipe is not significant, for inclined straight pipe, the pressure drop of the pipeline increases slowly first but then increases sharply with the increasing inclined angle, the turning point is the pipe inclination angle of 60 degrees. Thirdly, the migration of large pebbles in the pipeline is mainly manifested in three forms: sliding, rolling and jumping, and different pebbles have different migration patterns in different pipelines.

Automated summary

In this study, a three-dimensional transient slurry-pebble numerical model was established based on CFD-DEM coupling to analyze the flow characteristics of slurry shield pipeline system in sandy pebble stratum. The results showed that the critical velocity of pebble varied with particle size and shape, and the pressure drop in the pipeline was influenced by slurry velocity and pipe inclined angle. The migration of large pebbles in the pipeline was observed to occur through sliding, rolling, and jumping, with different patterns for different pebbles in different pipelines.