Hydro-Mechanical Properties of an Unsaturated Frictional Material

78 CHAPTER 4. EXPERIMENTAL SETUPS
190
5
15 60
80
45
Air pressure supply ua
Valve
Loading piston
20
110
54.25 15 54.25
Pressure transducer (optional)
70
Dial gauge
Porous stone
Soil specimen
Ceramic disk
Water reservior
Valve
Water pressure supply uw
Burette
Figure 4.2: Cross sectional area of the modified pressure plate apparatus (all dimensions in
mm)
oedometer cells the modified pressure plate apparatus permits to investigate one dimensional
compression and rebound behavior of soils under controlled suction.
Granular materials show a relatively small range of suctions over which the soil becomes
unsaturated. A low air-entry value is characteristic for this type of materials. To be able to
apply low suction the cell allows for the use of the hanging water column technique (Haines
1930). By lowering the attached burette with respect to the top of the ceramic disk and
using the scale with a resolution of 1 mm, suctions up to 4.0 kPa in steps of 0.1 kPa may
be applied to the specimen. The burette has a resolution of 0.05 cc enabling precise readings
of water inflow and outflow. Suctions up to 100 kPa may be applied to obtain test results
along the soil-water characteristic curve. The air pressure is applied to the top of the cell
using the axis-translation technique (Hilf 1956). Detailed literature review regarding hanging
water column and axis-translation technique for control of suction in a soil was presented