Transient measurement of hydraulic properties of unsaturated soils

Abstract

Many geo-environmental problems involve the study of mass flux of contaminants transported to the groundwater system through the unsaturated soil zone above ground water table. These problems always happen near the ground surface, so the estimation of permeability of unsaturated soil is of paramount interest.

The objectives of the project are to evaluate models used to determine coefficient of permeability of unsaturated soil. The outflow method developed by Gardner (1956) was evaluated and used as direct measurement of unsaturated permeability. Twelve existing models for unimodal unsaturated permeability and three proposed models for bimodal unsaturated permeability were evaluated with measured data. Three new models namely, SCM ,SBM and SMM were proposed by combing available SWCC (i.e. Satyanaga) and available integration methods (i.e., Childs and Collis-George, Burdine and Mualem).

Results from the study show that outflow method provides good prediction for unsaturated permeability of soil. The models for soil with unimodal characteristic were able to estimate the measured unsaturated permeability of soils with unimodal characteristic. Three proposed models performed quite well in describing the bimodal characteristics of soil.