Tensiometer saturation and the reliable measurement of soil suction

Recent advances in the technology for measuring matric suction have permitted the direct measurement of gauge pore water pressures lower than -100 kPa-that is, absolute tensions. This significant accomplishment has opened up a realm of research possibilities into the nature and behaviour of unsaturated soils. However, the widespread exploitation of this technology has been limited by the lack of a commercially available tensiometer capable of measuring high suctions, and by the complex and highly experience-driven nature of the filter saturation process. Much of the research on the direct measurement of matric suction has focused on achieving the maximum attainable suction value with high-pressure-range devices and large saturation pressures. However, there are many applications in physical modelling and laboratory testing where smaller suction ranges are of interest (< 400 kPa), illustrating the need for more sensitive, lower-pressure-range devices. As a consequence of the lower pressure range of these devices, the devices cannot be subjected to the high saturation pressures described in the literature. As a result, additional investigations into the processes involved in filter saturation are required. This paper investigates the importance of high initial saturation, and presents conditions for quality-assured suction measurements.