Water retention curve (WRC) is an important tool to study the hydraulic and mechanical properties of unsaturated soils

such as permeability

strength and deformation properties. Most of the existing WRC models fail to reflect the water retention mechanisms of unsaturated soils or they are complex in form

and these models are hard to give good performance on modelling the bimodal and multimodal WRCs. In this study

based on analyzing the water retention mechanisms of unsaturated soils

the WRC was divided into two domains that are governed by adsorption and capillary mechanisms

respectively. An adsorption water retention curve model (WRCM) was developed based on micro-pore filling theory and Kelvin’s law. A capillary WRCM was established based on the capillary condensation theory and Young-Laplace equation. Then

a new water retention curve model over the full suction range was built by superposing the adsorption and capillary WRCMs. Finally

the new model was validated through modelling the experimentally measured WRCs of six representative unsaturated soils

including Shanghai soft clay

Xi’an loess

Nanyang expansive soil

Guilin lateritic clay

Western Liaoning aeolian soil and Inner Mongolia Gaomiaozi (GMZ) bentonite. Results showed that the proposed model

which was simple in form with definite physical meaning parameters and successfully reflected the adsorption and capillary mechanisms of water retention

was able to simulate WRCs with different shapes for different types of soils under different conditions.