The Clogging Mechanism Of PVD Under Vacuum Preloading Based On CFD-DEM Approach

Vacuum preloading combined with the prefabricated vertical drains(PVDs)is one of the well-established technologies for soft ground improvement.However,clogging problem is frequently observed in the process of vacuum preloading,which causing the decrease of drainage efficiency and leading to an unsatisfactory reinforcement result.Thus,understanding and quantifying the clogging processes of PVDs are of great importance.In this paper,the clogging phenomenon was simulated based on CFD—DEM approach.Besides,a model test was also carried out to investigate the clogging phenomenon.Based on the model test and simulation,the clogging mechanism was discussedIn the first part,the process of cohesive sediment settling and flocculation was modeled based on CFD—DEM approach.In the model,the cohesiveness of the sediment particle was modeled by implementing the van der Waals force.In the simulation,the influence of Hamaker constant and polydispersity was investigated.And the flocculation phenomenon of cohesive particles was studied.The simulation results were in good agreement with the experimental results,which demonstrated the ability of the current model to study the clogging phenomenon.Then,a model test was carried out to investigate the clogging mechanism of the PVDs.In the test,the soil displacement field around the PVDs was observed by PIV method.Two different methods were proposed to quantifying the boundary of clogging area.In addition,the PTV method was used to track particles with different diameters and their relative displacement was obtained.According to the experiment results,it was found that the main reason for the clogging problem was that the small particles’ displacement was larger than large particles’,which lead to the formation of dense clogging layer on the surface of PVDs.Finally,the particle movement of dredge fill near the PVDs was simulated during the vacuum preloading process.The influence of initial soil moisture content,particle mean diameter and vacuum pressure on the clogging phenomenon was investigated.It was found that the simulation results were consistent with the experimental results.In this paper,model test and numerical simulation are carried out to study the clogging mechanism of PVDs under vacuum preloading,and to provide theoretical guidance for solving the clogging problem of PVDs in engineering.