Hydro-Mechanical Properties of an Unsaturated Frictional Material

84 CHAPTER 4. EXPERIMENTAL SETUPS
between the bottom plate and the plexiglas tube prevent from leakage. A tube with a valve is
connected to the water reservoir below the ceramic disk. By using a cylinder attached to this
tube the water outflow is measured. At all 6 openings (3 openings for tensiometer sensors, 3
openings for TDR sensors) enable to equip the specimen with tensiometer sensors as well as
TDR sensors. In 3 depths along the column 2 openings are installed opposite to each other.
The openings are installed equally spaced (see Fig. 4.9). In three layers with a distance of
60 mm pairs of tensiometer and TDR sensors are placed to measure simultaneously pore-
water pressure and volumetric water content in the specimen during the experiment. The
same tensiometer sensors and TDR sensors used for column testing device I were used for
column testing device II.
4.5 UPC Controlled-Suction Oedometer Cell
One dimensional compression and rebound tests and collapse tests were performed by using
the controlled-suction oedometer cell (Fig. 4.10). Similar to the modified pressure plate
apparatus the cell allows to apply suction to the specimen and to keep the suction constant
during the testing procedure.
The controlled-suction oedometer cell is also equipped with a burette and a scale with the
same accuracy as the equipment for the modified pressure plate apparatus, one air-pressure
system for application of matric suction as well as one air-pressure system for application of
vertical net stress. The application of matric suction to the specimen is equal to the procedure
used in the modified pressure plate apparatus (i.e. hanging water column technique, axis
σ*
σ*
- Air pressure system - ua Air pressure Burette - uw Scale Dial gagesystem
- Supply
Figure 4.10: Controlled-suction oedometer cell
Supply - ua Supply - uw
cell oedometer Controlled-suction