Modification of volumetric pressure plate extractor

Abstract

A volumetric pressure plate (extractor) can be used to measure the soil-water characteristic curve in the laboratory using the axis translation technique. The volume of extracted water from the soil specimen in the volumetric pressure plate can be continuously measured during the test without the stoppage of air pressure during the measurements. However, the water volume measurement in the volumetric pressure plate requires an air trap, a ballast tube, a burette, and a vacuum device while maintaining a constant pore-water pressure in the soil specimen, which is quite complicated and tedious. In order to improve the measuring method of the volumetric pressure plate, a modified volumetric pressure plate was developed and tested on residual soil specimens. The modified apparatus can measure the volume of the extracted water using both Method A and Method B of ASTM D6836-02 depending on the range of matric suction. In addition, the volume of diffused air during testing can also be measured for correcting the water volume change measurements. The improvements of the modified apparatus and typical results obtained from the tests are discussed in the paper.