ABSTRACT
Water has a major influence on the mechanical response of geomaterials and hence on the roads, railways or taxiways built on them. Water flow is usually modelled by solving the Richards equation with appropriate hydraulic conductivity functions and water retention curves for the soil. When materials are unsaturated, this approach means that water flow will be based on capillary concepts. In finer materials this is a good approach, but for coarser, open-graded, materials such as some granular road bases, some sub-bases and railway ballast, gravity forces have a significant influence on the pore water distribution and a notable impact on water flow, while the capillary term is much less significant. In order to get a general expression for both coarse and fine materials new formulations for the hydraulic properties and for the Richards equation are presented and discussed. A new expression for the unsaturated hydraulic conductivity is suggested, dividing the capillary term and the gravity term and including them in a slightly modified form into the Richards equation. The new expression is applied to an existing physical model for the unsaturated waterflow on coarse glass beads. The results are compared and discussed.
