Mesoscopic analysis and model test on formation process and state division of slurry membrane

In the slurry shield construction, slurry membrane forms when slurry invades stratum under high pressure. The mechanism of slurry membrane formation is complicated, but the criteria for the state division are relatively easy. A model of fluid-particle interaction and intergranular long-range attractive force is developed based on the discrete element program YADE to analyze the packing state of slurry particles during the initial constant rate period from the viewpoint of partical diameter ratio, Van der Waals force, initial fluid velocity and slurry particle density, to determine the lower limit value of slurry membrane state corresponding to the closest packing of soil particles. The slurry membrane state with two diameters of soil particles is also analyzed by conducting the model test using the slurry after standing. The result of model test shows that the influence of partical diameter ratio on slurry membrane state is consistent with the DEM simulation and the theory of state division of slurry membrane. The macro-meso relation is established for slurry membrane formation process. This study remedies the defects of the conventional filtration theory and DEM simulation which do not consider slurry invading stratum and slurry membrane forming dynamically.