Method of Swelling Pressure Measurement Using Large Pressure Plate Apparatus

by

Professor Jun Wu

(Laboratory of Joseph W. Stucki, University of Illinois)

1. Apparatus and Equipment

     a.  Tank of compressed nitrogen.

     b.  Pressure reducer-regulator—with primary gauge 0-3000 psi & 2^nd gauge 0-400 psi.

     c.  Fine pressure regulator—0-300 psi.

     d.  Accurate pressure gauge—0-250 psi with one small scale division=0.5 psi.

     e.  Sample holder—Thin walled metal cylinders(rings) with a sharpened edge on one end, diameter=5-8 cm, height=2-3cm.

     f.   15 bar ceramic plate extractor—Product of Soil-moisture Equipment Corp., P. O. Box 30025, Santa Barbara, CA 93105.

2. Setup

     Connect the apparatus in the sequence as following:

     a.  Compressed N₂-tank----Pressure reducer-regulator----Fine pressure regulator----Pressure gauge (as a bypass using 3-way connector)----2-way open-close-valve----Big pressure vessel of the 15 bar ceramic plate extractor.

     b.  Connect the external part of the outflow tube from the pressure vessel to the tip of a burette.

     c.  Make sure that all piping and connectors are leak free.

3. Procedure

     a.  Fasten a piece of cheesecloth to the lower end of each sample holder with a rubber band.

     b.  Prepare duplicate of required amount of sample, which varies with sample nature, and put into sample holder.

     c.  Have each sample in holder fully saturated with water.

     d.  Wet the ceramic pressure plate with a thin layer of water and put the sample holders on the plate, make sure that there is a good contact between the lower part of the sample and the surface of the ceramic plate.

     e.  Remove the excess water from the ceramic plate surface with a syringe, connect the outflow tube of the pressure cell to the pass-through connector in the wall of the vessel.

     f.   Put some vacuum grease on the O-ring, mount the lid and screw down clamping bolts.

     g.  Build up the pressure in the vessel slowly to the set point and keep the set pressure constant until the equilibrium is reached (usually it takes 2-3 days depending on sample).

     h.  Samples may be removed when readings on the outflow burettes indicate flow has stopped and equilibrium reached.

     i.   Remove the external tubes from the outflow tube assemblies to prevent possible back flow of water when the pressure in the vessel is released.

     j.   Determine the water content of the sample as soon as the pressure was released and the vessel lid was removed

4. Result

    The pressure applied is equal to the swelling pressure of the sample at the water content determined.