Microporous Membrane Technology for Measurement of Soil-Water Characteristic Curve

High air entry ceramic disks are commonly used for the control of matric suction in triaxial and direct shear tests and in tests for obtaining the soil-water characteristic curve. Geotechnical engineers have made increasing use of high air entry ceramic disks in order to measure or control matric suctions during unsaturated soil testing. One of the limitations associated with the use of high air entry ceramic disks has been the time required in order for equilibrium conditions to be established across the disk. Improving the efficiency associated with establishing suction equilibrium is of considerable interest to geotechnical engineers. Pressure membrane technology involving the use of microporous membranes is one possible technology that could result in improved performance for the measurement or control of matric suctions. If microporous membrane technology can be used, the end result could provide considerable time and cost savings, particularly in the measurement of soil-water characteristic curves (SWCCs). In this study, a new apparatus was developed to make use of a microporous membrane for the measurement of the SWCC with matric suction of up to 25 kPa. The maximum AEV (i.e., air-entry value) of the membrane is 250 kPa. This paper presents the results of laboratory SWCC measurements on several soil types using pressure membrane technology. Comparisons are made between the soil-water characteristic curies measured using a conventional pressure plate apparatus and those obtained from the new micro membrane apparatus.