Estimation of unsaturated hydraulic conductivity function: implication of low to high suction measurements

Establishment of the relationship between soil suction and water content, commonly termed as soil-water characteristic curve (SWCC), is of prime importance in the field of unsaturated soil mechanics. There are several instruments available that can be used to measure the SWCC of soil, but every suction measuring device has its own limitations in terms of its suction measurement range. Therefore, the preciseness of the estimated unsaturated soil properties largely depends on the range of suction measurements and the type of instruments used. The primary objective of this study is to quantify the error that can occur during the estimation of unsaturated hydraulic conductivity function (UHCF) from SWCC for low plastic soils. Experiments were performed to investigate the influence of different suction measurement devices on the estimated UHCF for four different soils with varying clay content. A dew point potentiometer (WP4) and a miniature tensiometer (T5) have been used in this study for the suction measurement. The SWCC of the selected soils were predicted mathematically using a commonly used pedo-transfer function (PTF). The experimental results clearly indicated that the sole use of WP4 overestimated the SWCC parameters, as well as UHCF (overestimation in the conductivity value is in order of 10(4) times). Rather, a combination of T5 and WP4 data, within their accurate range, provides a more precise estimation of UHCF. Further, the accuracy of the PTF was found very effective for low plastic soils with a relatively low percentage of clay (% clay < 10), in the absence of any experimental data.