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Title: Suction measurements and water retention in unsaturated soils
Author: Lourenço, Sérgio Duarte Nunes
ISNI:       0000 0001 3612 9912
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 2008
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Techniques for testing unsaturated soils have been investigated by the author where the measurement and control of parameters were undertaken directly. Suction was measured and controlled with a new high suction tensiometer and water content through mass measurements with a balance. These techniques have been used for the determination of soil water retention curves and for the development of a suction . control system using air circulation and water injection. The techniques allow the soil to be subject to the same drying and wetting conditions that occur in nature and avoid the need for elevated air pressures, as are traditionally involved in testing using the axis translation technique. The performance of the new high suction tensiometer was evaluated, followed by its applications to soil testing. The tensiometer performance focused on the factors controlling cavitation, calibration in the negative pressure range and measurement. It was found that isotropic unloading is the most accurate technique for calibration in the negative range and that axis translation techniques can lead to errors. The research confirms high suction tensiometers are easy to use and versatile devices. Techniques were developed to measure and control suction and water content in unconfined and confined samples. Research on the unconfined samples focused on the procedures to obtain the soil water retention curve: discrete (soil dried or wetted in stages) and continuous (soil drying continuously). While both procedures were found not to influence the curves significantly, it is demonstrated that the continuous procedure is sensitive to factors such as the exposed surface area to drying or wetting and so should be used carefully. For confined conditions, wetting, drying, and water content measurement systems were developed. Wetting was based on the injection of water; drying was based on air circulation through a desiccant within a closed loop system. Water content was determined from the. difference between water injected and that adsorbed by the desiccant. This has been applied as part of a· double cell triaxial testing system that allows continuous determination of suction, water content and volume change. A challenge of such a system was imposing an air tight environment. The suitability of environmental scanning electron microscopy to observe unsaturated soils at the particle level was explored. The imaging of micron-sized materials at different relative humidities allowed a series of observations previously undocumented, among them: water menisci were visible, including their shape and interaction with surfaces; the contact angle between the air-water and water-solid interfaces was measurable.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available