Effect of bimodal soil-water characteristic curve on the estimation of permeability function

Soil-water characteristic curve (SWCC) defines the relationship between water content and suction in soil. Many unsaturated properties can be estimated from SWCC such as permeability function and unsaturated shear strength. Therefore, SWCC is considered as the key information of unsaturated soil properties. Permeability function, which defines the relationship between hydraulic conductivity and matric suction, is essential information for seepage analysis in understanding water flow in unsaturated soil. The permeability function is commonly determined indirectly from the SWCC rather than from direct measurement in the laboratory because the direct measurement is time consuming and costly. On the other hand, it has been reported that SWCC can have unimodal and bimodal characteristics. Many models have been proposed for the estimation of permeability function from a unimodal SWCC while limited numbers of model have been proposed for a bimodal SWCC. In this paper, experimental works in laboratory were carried out for measurements of the unsaturated permeability of soils with bimodal SWCC. Zhai and Rahardjo's (2015) equation was used to estimate the permeability function of soils with bimodal SWCC. The experimental results show good agreement with the estimated permeability function. Therefore, Zhai and Rahardjo's (2015) equation was recommended for the estimation of the permeability function from bimodal SWCC. This study also shows that the variability in bimodal SWCC has significant effect on the estimation of the permeability function.