  Water retention is one of the key soil characteristics. Available models of
soil water retention relate to the curve-fitting type. The objective of this
work is to suggest a physical model of water retention (drying branch) for
soils with a rigid matrix. "Physical" means the prediction based on the a
priori measured or estimated soil parameters with a clear physical meaning. We
rely on the two-factor model of clay that takes into account the factors of
capillarity and shrinkage. The key points of the model to be proposed are some
weak pseudo shrinkage that the rigid soils demonstrate according to their
experimental water retention curves, and some specific properties of the rigid
grain matrix. The three input parameters for prediction of soil water retention
with the rigid grain matrix include inter-grain porosity, as well as maximum
and minimum grain sizes. The comparison between measured and predicted sand
water retention curves for four different sands is promising.
