A water retention model considering biopolymer-soil interactions

Biopolymer treatment has been considered as one of the most sustainable methods of soil improvement for controlling subsurface water flow. It is able to alter pore structure and hence water retention behaviour of soils, as demonstrated by extensive experimental results in the literature. To predict the effects of biopolymer treatment on the surface and subsurface water flow, it is important to develop a proper water retention model for biopolymer-amended unsaturated soils. The existing models do not consider the complex biopolymer-soil interactions. In this study, a new soil water retention model is developed with a consideration of various mechanisms of biopolymer-soil interactions, including (1) biopolymer occupies some pore space and therefore changes the pore volume of soil; (2) biopolymer itself is able to hold water; (3) the swelling of biopolymer may induce soil volume change; (4) the swelling of biopolymer is partially constrained by soil particles. To verify the new model, it is applied to simulate the measured water retention curves of seven soils. The measured and calculated results show good agreement. It is convincingly demonstrated that the new model is able to well capture the water retention behaviour of various soils amended by different biopolymers.