Hydro-Mechanical Properties of an Unsaturated Frictional Material

104 CHAPTER 5. MATERIAL USED AND EXPERIMENTAL PROGRAM
1. Placing the water table in the burette to the height of the bottom of the sand specimen
(h0 = 0 cm).
2. Open all valves (i.e. ua = atmospheric pressure).
3. Lowering the water table down (e.g. h1 = −30 cm that is equal to ψ = 3 kPa) by using
the burette with reference to the bottom of the specimen (h0) and using the attached
fixed scale.
4. Due to applied suction water is flowing out of the specimen. Hence the water table has
to be adjusted continuously by lowering the water table back to h1.
5. Repetition of the procedure 4. until equilibrium state is reached (no water flow observed).
The pressure mode test realized the application of suctions larger than 4 kPa. The application
of suction using pressure mode test includes the following steps:
1. Connection of the upper valve to an air-pressure system.
2. Placing the water table in the burette to the height of the bottom of the sand specimen
(h0 = 0 cm).
3. Application of air-pressure (e.g. ua = 10 kPa that is equal to ψ = 10 kPa).
4. Open all valves.
5. Due to applied suction water is flowing out of the specimen. Therefore the water table
has to be adjusted continuously by lowering the water table back to h0.
6. Repetition of the procedure 5. until equilibrium state is reached (no water flow observed).
Generally during drainage process water is flowing from the specimen into the burette. When
wetting the specimen water is flowing from the burette to the sand specimen. The change
of water table in the burette during all induced suction steps was carefully obtained. The
final gravimetric water content was calculated by oven-drying the specimen at the end of the
test. Volumetric water contents, degree of saturations and gravimetric water contents corre-
sponding to each suction step were back-calculated from these final values using incremental
amounts of water flow from each applied step.
Specimen preparation and testing procedure - column device I
Loose and dense specimens with a height of about 540 mm and 300 mm in diameter were
prepared by uniformly pluviating oven dry sand with a funnel (500 ml capacity) into the
column filled with deaired water, thus ensuring almost 100% saturation. The deaired water
was continuously injected into the cell by using the pump attached to the water reservoir at