Percolation theory and hydrodynamics of soil-peat mixtures

Great quantities of organic matter are added reconstituting soils in urban conditions. To evaluate the efficiency of organic matter on physical proper ties of reconstituted soils, we studied the effects of loading on intrinsic permeability of soils mixed with peat. Percolation theory associated with a statistical porosity approach was used to explain variation of permeabili ty related to porosity. After compression, sample porosity was measured and the pore-space morphology described by image analysis. An ellipse with maj or axis (a) and minor axis (b) was inscribed within each pore. All the pore s appeared as lenses of different sizes which could be assumed to represent disk-shaped cracks characterized by a diameter d and an aperture e. The cr ack model was calculated by means of a percolation threshold, p(c) = 0.33, along with values d and e as well as the measured porosity. This allowed a determination of the crack interconnection factor f. During compression, th e number of pores per unit area decreased. Increasing the loading closed of f pores and modified flow pathways. Connected sites facilitating percolatio n became disconnected from each other and the now was reduced. The effectiv e porosity, which actually took part in flow, was determined for all the sa mples and was dependent on peat content.