Hydraulic Conductivity Measurement in Unsaturated Soils with a Modified Cone Penetrometer.

In this project, a new cone penetration test CPT method for the determining the hydraulic properties of unsaturated soil was developed. A modified cone penetrometer cone permeameter is used to inject water into the soil under constant pressure through a screen and measure movement of the wetting front with tensiometer rings. An inverse methodology is used to analyze the cumulative inflow volume and pressure head readings to obtain estimates of the hydraulic conductivity and soil moisture retention curves for the soil. To accomplish the inversion, a cone permeameter test is numerically simulated with the radially symmetric form of Richards equation and the van Genuchten hydraulic conductivity and moisture retention functions. An objective function expressing the differences between flow responses measured with the cone permeameter and those predicted using the numerical model with the parameterized soil hydraulic properties is minimized to obtain the hydraulic parameter estimates. Full scale tests in a laboratory aquifer and field tests were performed during the course of this study. Excellent agreement between saturated hydraulic conductivity values obtained with the cone permeameter and values from in-situ Guelph permeameter and laboratory falling head tests was obtained. Soil moisture retention curves were similar to those obtained from multi-step outflow and capillary rise tests.