The driving force of liquid flow in a granular material is divided into two components, one is the capillarysuction potential and the other the osmotic suction potential.
When the granular material consists of large particles (e.g. unconsolidated sand in the sieve range), themovement of water in the bed is caused by the capillary suction potential difference, while for small particles (e.g. clay), the osmotic suction potential becomes predominant.
Here, the method of measuring the capillary suction potential is mainly described, and the result of experimentsas follows:
1) Effects of particle size and voidage of beds on the capillary suction potential (Fig. 6, 7), and the hysteresisof water movement in beds (Fig. 9, 11) were studied.
2) Correlation between temperature-and the capillary suction potential was-found as
p (φ,
t)=
p (Φ,
t0)δ/δ
0, (Fig. 8).
3) Glass sphere beds with various moisture contents were prepared and the capillary suction potentials weremeasured for each bed. Based on these, the drainage and imbibition curves were obtained (Fig. 12, 13).
These curves were entirely different from the well-known curve for the gradual drainage starting froma saturated bed.
The osmotic suction potentials were obtained by simple measurements of clay bed (Fig. 15).
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