A simple water retention model of dual-porosity soils based on self-similarity of bimodal pore size distribution

Abstract

The bimodal characteristic of water retention curves of dual-porosity soils has been fully recognized, however, the excessive number of fitted parameters in the existing models limits their application. This study develops a simple water retention model for dual-porosity soils that considers the self-similar characteristics of the pore size distribution (PSD) between macropore and micropore regions. In the model, we simulate the macropore PSD by differential VG model, which is then shifted and scaled to capture micropore PSD. It is hypothesized that the bimodal PSD can be obtained by superimposing the PSDs of macropore and micropore regions to derive the bimodal water retention curve (BWRC). The mercury intrusion porosimetry (MIP) tests and water retention tests are conducted on Nanyang clay with three different dry densities to evaluate the proposed BWRC. The results show that the new parameter can be determined by the MIP dataset and then used to predict the water retention behavior of dual-porosity soils well. Finally, we also explore the application of the proposed BWRC in predicting the hydraulic conductivity of dual-porosity soils without adding any extra parameters.