Modeling of permeability for granular soils considering the particle size distribution

A model was proposed to predict the permeability of granular soil with various gradations. The pore size distribution for different particle sizes was determined by considering different particle combinations and occurrence probabilities, which was then used in the fractal and capillary model for predicting soil permeability. The proposed model was verified by experiments and exhibited higher accuracy than other models. Upon verifying by over 60 tests, the mean absolute percent error using this proposed model was 18% for the permeability predictions of spherical granular soils. The pore size distribution predicted by the model was verified by computed tomography to capture the pore characteristics of different soil gradations. The proposed model only requires three parameters (soil particle size distribution, void ratio, and relative density) to predict soil permeability, and no empirical or calibrated parameters are needed. A parametric analysis showed that the gradation significantly affected soil permeability. Even when porosity and the characteristic particle size, d(50), are the same, as the particle size distribution narrows and the gradation range decreases, the permeability coefficient can increase by 80%. The permeability increased with the void ratio and decreased as the relative density increased. The proposed model provides a practical approach for predicting the permeability of granular soils and considers the effect of the particle size distribution.