Semi empirical hydromechanical model for quantifying effectiveness of loaded granular filters

This paper presents results from a series of filtration tests to investigate geometrical and hydromechanical factors controlling the erosion of base particles and their subsequent capture into sand-gravel filters subjected to uniaxial static loading. The analysis revealed that the effectiveness of a filter, apart from its geometry (i.e. particles and constriction sizes), is also controlled by unique combinations of associated hydromechanical factors such as applied hydraulic gradients and the resulting effective stresses. Furthermore, it is observed that the base soil experiences a significant and continuous reduction in effective stress during internal flow (seepage), and the migration of base particles into the filter initiates after localised fluidisation in the base soil (i.e. at very low effective stress levels). Based on limit equilibrium considerations, a novel theoretical approach, different from all other existing methods, is proposed to estimate the critical hydraulic gradient for base soil erosion into granular filter and hence the retention capacity of filters. The current methodology is subsequently validated using experimental data from the published literature and promising results were obtained.