ESTIMATION OF UNSATURATED SOIL PARAMETERS FROM INFILTRATION AND INTERNAL DRAINAGE TESTS

Abstract

Moisture movement in the unsaturated zone is important in agricultural engineering, soil science, ground water recharge assessment and environmental engineering. Knowledge of unsaturated soil parameters is essential for the analysis of moisture flow in the unsaturated zone. Soil in the unsaturated zone is characterized by the presence of voids, which are partly filled with water and partly with air. Water is held in the voids due to the surface tension forces. The pressure in the unsaturated zone is always less than the atmospheric pressure. The flow in the unsaturated zone is basically a multi phase flow i.e. both air and water moves simultaneously in the void space. Movement of water vapor also takes place. The present study involves the estimation of unsaturated soil parameters using direct and indirect methods. The direct method involves estimation of unsaturated soil properties from particle size distribution data and moisture content pressure head relationship. The indirect method involves estimation of parameters by an optimization algorithm by minimizing the deviations from observed and predicted infiltration rates of infiltration test and moisture contents by internal drainage test and internal drainage test. For saturated hydraulic conductivity determination GUELPH permeameter is used. Soil moisture meter is used for the suction head reading measurement and Time Domain Reflectometer is used for moisture content measurement. The indirect method is solved by using the Levenberg-Marquardt algorithm. The parameters obtained by both the methods are compared and advantages of each method are discussed.