Study of hydraulic properties of binary beads mixture as porous media in sustainable urban drainage system

Sustainable Urban Drainage System (SuDS) such as swales and rain gardens is showing growing popularity as a green technology for stormwater management and it can be used in all types of development to provide a natural approach to managing drainage. Soil permeability is a critical factor in selecting the right SuDS technique for a site. On this basis, we have set up a laboratory experiment to investigate the porosity and saturated hydraulic conductivity of single size and binary (two sizes) mixture using column-test as a preliminary investigation with two sets of glass beads with different sizes are used in this study. The porosity and saturated hydraulic conductivity for varies volume fraction of the course and fine glass beads were measured. It was found that the porosity of the binary mixture does not increase with the increment of the ratio of coarse to fine beads until the volume fraction of fine particles is equal to the coarse component. Saturated hydraulic conductivity result shows that the assumption of random packing was not achieved at the higher coarse ratio where most of the fine particles tend to sit at the bottom of the column forming separate layers which lower the overall hydraulic conductivity value.