Continuum percolation theory for water retention and hydraulic conductivity of fractal soils: estimation of the critical volume fraction for percolation

Systematic experimental deviations from theoretical predictions for water retention characteristics of fractal porous media develop at a moisture content, θd. Below θd larger suction pressures are required than would otherwise be predicted from the implied fractal pore-size distribution. Inferred values of θd were shown to be compatible with observed values of the volumetric moisture content, θt, at which solute diffusion vanishes. The comparison was based on an accurate phenomenological result for θt. The approximate equivalence of the two moisture contents was interpreted in the context of continuum percolation theory (at low moisture contents, below a critical volume fraction of water, αc, connections for capillary flow are interrupted, leading to a near vanishing of solute diffusion and increasing enormously the time required for equilibration to new pressures). The experimental results for θd are now investigated to determine whether their values are generally compatible with theoretically based estimates for αc.