Size segregation mechanism of reclamation fill sand due to rainbowing operations in hydraulic dredging activities

Abstract

Segregation of sand grains is often detected in reclamation lands constructed by hydraulic dredging activities using various placement methods, such as bottom dumping, rainbowing, and discharging via floating pipelines. Heterogeneities in the geotechnical characteristics of the reclamation land, such as the relative density, the hydraulic conductivity, and the shear strength, are caused by the size segregation of the dredged materials. In this paper, a computational fluid dynamic (CFD) method and the discrete element method (DEM) are coupled to investigate the mechanism of size segregation of the dredged sands in the deposit process after the rainbowing operations. A numerical water tank is established with an initially uniform flow field. The sand grains are jetted from the nozzle at a given velocity and are then deposited under their self-weight and the drag force from the atmospheric water. The numerical model is validated through a simulation of the settlement of single grains. The main factors that influence the size segregation phenomenon—the flow velocity, the rainbowing velocity, and the water depth—are investigated based on a parametric study. The complex interlayers observed in real reclamation lands are reproduced by considering the construction sequence of the dredged materials.