Reliability of HCT-based SWRCs

Meghdad Bagheri, Damilola Akinniyi, Vasileios Matziaris

Research output: Chapter in Book/Report/Conference proceedingConference proceedingpeer-review

Abstract

The mechanical behavior of unsaturated soils is greatly influenced by pore-water tension, known as soil suction, and the water retention characteristics of the soil. Among various laboratory methods reported in the literature, the use of high-capacity tensiometers (HCTs) for measurement of soil water retention curve (SWRC) has received significant interest in the most recent studies. Consequently, there have been several design and experimental procedures developed for measurement of HCT-based SWRCs. However, despite these developments, the accuracy, range and duration of HCT-based measurement is still largely characterized by uncertainties and inconsistencies, thereby, reducing the reliability of the obtained SWRCs. In this work, an experimental program is designed to address these uncertainties. Gravimetric water content based SWRCs of reconstituted London clay were measured using the continuous drying (dynamic) method with evaporation rate control. Specimens confined in an oedometer cutting ring were placed on a digital balance and subjected to controlled air drying at ambient temperature. The variations of soil suction in the specimens were simultaneously recorded by four in-house designed HCTs placed at the mid-height of the specimens. A total of six tests were carried out and the obtained SWRCs were analyzed based on the maximum suction value recorded by HCTs (smax), the obtained air-entry value (saev), the suction at inflection point (si), the water content at inflection point (wi), and the slope of tangent to inflection point (mi). A percentage uncertainty of ±4% was obtained for the saev and si values. Similarly, percentage uncertainties of ±6% and ±0.5% were obtained respectively for the mi and wi values. These results were further compared with parametric analysis of the reported SWRCs of the same soil in the literature. Given the observed tolerance ranges, cautions must be taken in selecting values for these parameters e.g. as input values in mathematical curve fitting equations for prediction of the entire SWRC, or in unsaturated constitutive modelling, to enhance reliability of the outputs. Furthermore, a minimum of two HCTs was deemed necessary for more accurate and reliable measurement of SWRCs.
Original languageEnglish
Title of host publication8th International Conference on Unsaturated Soils
Publication statusIn preparation - 2022

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