Hydro-Mechanical Properties of an Unsaturated Frictional Material

5.3. SPECIMEN PREPARATION AND TESTING PROCEDURE 103
To prevent air bubbles from accumulating in the water reservoir below the ceramic disk, the
system was periodically flushed with deaired water.
The testing procedure consisted of preparing an oven dry specimen with a predetermined
void ratio, as a fixed ring specimen. The specimens are 20 mm high, 70 mm in diameter and
where produced using a funnel with a capacity of 100 ml. When preparing loose specimens
the falling height was 0 mm and when preparing dense specimens the falling height was 100
mm (see Fig. 5.7). To achieve a plane surface the top of the sand specimens were planed
by using a metal sheet. The specimen was saturated by supplying water from the burette
through the bottom ceramic disk. Saturation process of the sand specimen means, that the
required amount of water was injected through the water reservoir and the ceramic disk by
using the attached burette. The saturation process was finished when the water level in the
burette reaches the top of the specimen and is left there for 10 hours equilibrium time.
The specimens were subjected to a predetermined matric suction using either a suction
mode test or a pressure mode test (i.e. axis-translation technique). All tests were started
at fluid saturated conditions. The experiments performed in the modified pressure plate
apparatus were steady state type tests. After the specimen had reached equilibrium (i.e. no
water inflow or outflow), it was subjected to the next suction increment. Suctions up to 4 kPa
were induced by suction mode test. This means that a hanging water column was subjected
to the sand specimen by using the attached burette and the attached scale. The bottom of
the specimen was used as a reference value, where the suction is equal to zero (h0 = 0 cm,
ψ = 0 kPa). Following steps for application of suction using hanging water column technique
were carried out:
Valve
Funnel
Sand
Sand specimen
Ceramic disk
Water reservior
Valve
Water pressure supply uw
Burette
Valve
Sand specimen
Ceramic disk
Water reservior
Valve
Water pressure supply uw
Figure 5.7: Preparation of loose (left) and dense (right) sand specimen in modified pressure
plate apparatus
10 cm
Funnel
Sand
Burette