A laboratory study of particle pickup characteristic for the circulation system of large-sized slurry shield

During a tunnelling construction with the application of slurry shield machine, the pipe blockage is generally regarded as a common technique problem in the slurry circulation system. In this paper, an experiment is conducted indoor with a large size slurry circulation system to observe the pickup motion. To better imitate the gravel accumulation in the real construction, the researching object is determined as multiple particles with three categories of ballasts, pebbles and spheres. Recorded by a high speed camera, the pickup movement is slowed and analyzed. Divided by the particle piling, the pickup motion could be divided into two forms particles transferring and integral movement. The result shows that the increasing particle size would also raise the critical velocity, while the increasing speed would simultaneously get decreased. The effect of categories on the critical velocity satisfies ballasts > pebbles > spheres, which also correspond to the shape irregularity. In addition, it is also found that the piling of particles would have a significant effect on the critical velocity, which might even exceed the particle sizes.