Numerical Determination of Unsaturated Hydraulic Conductivity From Time-Series Outflow Data

Abstract

In this study, the focus is placed on addressing the challenge posed by the time-consuming nature of experimental methods employed for the determination of the hydraulic conductivity function (HCF) in unsaturated soil. Instead, preference is given to transient inflow/outflow experiments utilizing the axis translation technique. Within this framework, the flow through specimens inside a suction-controlled oedometer is modeled as a one-dimensional unsaturated seepage problem, with consideration of ceramic impedance. The impact of suction-induced volume change on unsaturated flow is incorporated into the numerical model. A novel approach for estimating internodal conductivities in numerical simulations is introduced. The transient variation of soil water mass is monitored to collect time-series water content data. This data, in conjunction with a 1-D seepage model, are used to estimate the hydraulic conductivity function. The implementation of the numerical model is straightforward, and a spreadsheet can be employed for this purpose. Importantly, the experimental setup requires no special or expensive equipment beyond what is commonly used in unsaturated soil testing. To validate the proposed numerical model, experiments were conducted on various soil types, including poorly graded sand, non-plastic silt, and highly plastic clay. The predictions are subsequently validated against data obtained from existing, sophisticated HCF determination techniques, affirming the method’s effectiveness for estimating the hydraulic conductivity function in unsaturated soils.