BULK DENSITY DEPENDENCE OF AIR ENTRY SUCTIONS AND SATURATED HYDRAULIC CONDUCTIVITIES OF SOILS

The bulk density of a soil changes with natural and artificial processes in a field. The larger the bulk density ρb of the soil, the larger the air entry suction he and the smaller the hydraulic conductivity Ks. Although both the Kozeny-Carman equation, based on Poiseuille's law, and Campbell's method, based on a similar media concept (SMC) by Miller and Miller, are able to predict bulk density dependencies of hydraulic conductivities theoretically, the applicabilities and limitations of them have been vague. This paper proposes a non-similar media concept (NSMC) model, composed of a characteristic length for the solid phase S and for the pore phase d, and a shape factor τ of the solid phase, to predict he and Ks values of a given soil as functions of its ρb. By comparing the NSMC model with the Campbell method and the Kozeny-Carman equation, it was clarified experimentally that the NSMC model is applicable to aggregated soils in the predictions of he (ρb) and Ks (ρb) as well as to dispersed soils. The shape factor τ was close to 1 when the soil was dispersed and sandy, whereas it was close to ρb/ρs, ρs being the density of soil particles, when the soil was aggregated.