Hydro-Mechanical Properties of an Unsaturated Frictional Material

102 CHAPTER 5. MATERIAL USED AND EXPERIMENTAL PROGRAM
- Polishing at 20 µm for 15 min with adding water.
- Polishing at 15 µm for 15 min with adding oil.
- Polishing at 3 µm for 10 min with adding diamond paste .
- Cleaning of specimen in ultrasonic bath.
The distribution of void ratio of the horizontal area was observed using electron microscopy
(see Fig. 5.5). A digital camera attached to the microscopy took photos of the specimen, that
are further analyzed using image processing and analysis program. Binary filtered images
were used for determination of the void ratio (Fig. 5.5 right). The void ratio was determined
for 11%, 33%, 44% and 66% (see Fig. 5.6) of the total area (A = 2651 mm 2 ) as well as for
the total area. The determined void ratios of the areas varied from e = 0.71 to e = 0.76, that
leads to the results the void ratio is uniformly distributed over the investigated range.
Specimen preparation and testing procedure - modified pressure plate apparatus
Before each test the ceramic disk was saturated in a first step. To ensure full saturation of
the ceramic disk, deaired, deionized water was passed through the ceramic disk using an air
pressure of 70 kPa in the upper air compartment. The system was closed and opened in a
step-wise manner using the valves. The water outflow was collected in the attached burette
and the ceramic disk was assumed to be fully saturated when no air bubbles were collected in
the burette. All experiments conducted in the modified pressure plate apparatus were long
time tests (approximately 2 month for determination of one drainage or imbibition curve).
Figure 5.5: Electron microscopy (left), Hostun sand specimen hardened with epoxy resin
(middle) and picture of Hostun sand specimen after image analysis (right)
Figure 5.6: Investigated areas for determination of void ratio