Volume 22, Issue 3 (September 1999)
The Use of Miniature Pore Pressure Transducers in Measuring Matric Suction in Unsaturated Soils
Matric suction (pore air pressure minus pore water pressure) is an important stress state variable in unsaturated soil mechanics. Currently available devices to measure matric suction suffer from one or more of the following: bulky construction, long time to reach equilibrium, high sensitivity to temperature, and inability to produce continuous output. Tests were conducted using a miniature pore pressure transducer (PDCR81), traditionally used to measure positive pore water pressures in saturated soils, to measure matric suction in unsaturated soils. The results were compared with measurements from a conventional Bourdon-type tensiometer. Due to the small volume of fluid in the measuring chamber, the PDCR81 reached equilibrium much faster than the tensiometer and is more responsive to changes in pore water pressure. However, incomplete saturation produced greater errors in PDCR81 measurements. An increase in the saturation fluid viscosity of the PDCR81 increased the time to reach and maintain equilibrium.