Permeability reduction of soil filters due to physical clogging

Soil filters, which are commonly used to provide stability to the base soils in subsurface infrastructure, are prone to long-term accumulation of fine micron-sized particles. This causes reduction in the permeability, which in turn may lead to intolerable decreases in their drainage capacity. In this paper, the extent of this reduction is addressed using results from both experimental and theoretical investigations. In the experimental phase, a sandy soil commonly used as a filter or drainage layer was subjected to pore fluids containing polystyrene or kaolinite particles, and their permeability reductions were determined in terms of the pore fluid suspension parameters. In the theoretical phase of the investigation, a representative elemental volume of the soil filter was modeled as an ensemble of capillary tubes and the permeability reduction due to physical clogging was simulated using basic principles of flow in cylindrical tubes. The results from the experimental and theoretical investigations were in good agreement. In general, the permeability reduced by more than one order of magnitude, even when the migrating particles were smaller than the majority of the soil filter pores. The concentration of particles in the pore stream affected the rate at which the permeability reduced. Self-filtration of particles, which is prominent at higher flow rates, may itself lead to a 20% reduction in the permeability for these sands.