ESTIMATING SOIL HYDRAULIC PROPERTIES FROM TRANSIENT CONE PERMEAMETER DATA

Abstract

We present here a method for determining the hydraulic properties of unsaturated soil via inverse modeling. A modified cone penetrometer, called a cone permeameter, has been designed to inject water into the soil through a screen and to measure the progress of the wetting front with two tensiometer rings positioned above the screen. Cumulative inflow and pressure head readings are analyzed to obtain estimates of the hydraulic parameters describing the hydraulic conductivity curve K(h) and the soil-moisture characteristic curve, θ(h). Two sets of cone permeameter tests, which differ in the method of placement in the soil, are discussed. In the first case, the cone permeameter was buried; in the second case, it was placed by direct push to the testing depth. Optimizations for various sets of unknown parameters, with and without additional soil moisture information, were performed. The effects of applied pressure head at the source and of initial pressure readings on the resulting hydraulic parameters are investigated. The optimization results are compared with the results of standard laboratory and field methods. The saturated hydraulic conductivity was well estimated. For cases in which the saturated moisture content was estimated or fixed near the laboratory-derived value, the soil-moisture characteristic curves were between the wetting and drying curves obtained from other standard methods.