Development of Cone Penetrometer Method to Determine Soil Hydraulic Properties

Abstract

Effective cleanup of contaminated sites requires characterization of the hydraulic properties of impacted soils. To this end, we present a new method for estimating soil-water characteristic and hydraulic conductivity curves with a modified cone penetrometer. A prototype has been designed and fabricated with a screen close to the penetrometer tip and two tensiometer rings 5 and 9 cm above the screen. Water is injected into the soil under constant pressure. The volume of water imbibed into the soil is monitored, as are the tensiometer ring readings registering the advancement of the wetting front. These transient flow data are used to estimate soil hydraulic properties via numerical inversion of Richards' equation. We present the results of cone tests performed under variably saturated conditions in a laboratory aquifer system. Results are compared with independent measurements of the soil hydraulic properties to benchmark the performance of the instrument and method of analysis. The saturated hydraulic conductivity of the soil is well predicted by the method for saturated and unsaturated conditions. Further work is required to obtain good estimates of the other parameters describing the hydraulic properties of the soil.