Evaluation of Constant Head Infiltration Test Analysis Methods for Field Estimation of Saturated Hydraulic Conductivity of Compacted Clay Liners

Abstract

Field infiltration tests are commonly used to assess the hydraulic conductivity of low permeability materials such as natural clay barriers and compacted clay liners. The soils used for compacted clay liners are always partially saturated and require very long testing times to reach steady-state flow conditions. Consequently, because they are less time consuming, laboratory tests are usually preferred for construction quality control. Nevertheless, it is well-known that field tests are more representative of the clay liner because of the scale effect. This is why, since the 1980s, the main issues associated with field procedures have been studied and several methods proposed for testing low-permeability materials within short time periods. The proposed methods are based on early-time flow analysis in unsaturated conditions and have been applied to various compacted soils under field and laboratory conditions. To evaluate these methods, we carried out a comprehensive testing program using a hydraulic field infiltrometer method (sealed single-ring infiltrometer) and a laboratory rigid-wall permeameter method that reproduces surface field test conditions. The laboratory tests were continued until saturated hydraulic conductivity was obtained so that this value could be compared against the hydraulic conductivity estimated from early-time analysis on the same specimen. The obtained results show the influence of (a) the initial moisture content, (b) the sorptivity and hydraulic head on the early-time infiltration rate, and (c) the final estimated hydraulic conductivity. A comparison of analysis methods shows the limitations of some and tries to explain the reasons for such inadequacies in the description of early-time unsaturated flows. Nevertheless, the conclusions of our study show that conventional early-time analyses give a good estimation of saturated hydraulic conductivity within a short time period compatible with construction quality-control procedures.