Hydro-Mechanical Properties of an Unsaturated Frictional Material
Hydro-Mechanical Properties of an Unsaturated Frictional Material
Hydro-Mechanical Properties of an Unsaturated Frictional Material
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4.5. UPC CONTROLLED-SUCTION OEDOMETER CELL 85<br />
Figure 4.11: Cross sectional area <strong>of</strong> the controlled suction oedometer cell UPC<br />
tr<strong>an</strong>slation technique). The cell is equipped (see Fig 4.11) with a specimen ring 50 mm in<br />
diameter <strong>an</strong>d 20 mm high. Like the specimen in the modified pressure plate apparatus the<br />
specimen here is assumed to be homogeneous in void ratio <strong>an</strong>d in the distribution <strong>of</strong> water<br />
content (volumetric water content, saturation).<br />
The controlled-suction oedometer cell consists <strong>of</strong> 5 parts (top part, middle part, bottom<br />
part, membr<strong>an</strong>e including porous stone <strong>an</strong>d ceramic disk) <strong>an</strong>d is made <strong>of</strong> steel to prevent <strong>an</strong>y<br />
deformations <strong>of</strong> the cell itself. The bottom part is a steel plate including the ceramic disk.<br />
The ceramic disk used in this investigation has <strong>an</strong> air-entry value <strong>of</strong> 100 kPa <strong>an</strong>d may be<br />
replaced by <strong>an</strong>other one, e.g. by a ceramic disk with 500 kPa air-entry value for testing silty<br />
<strong>an</strong>d clayey soil or a porous stone for performing conventional tests (i.e. tests on saturated<br />
soil specimen). Directly to the specimen ring the bottom disk is placed. The steel plate<br />
also provides a water reservoir below the disk, that is connected to a burette. By using the<br />
burette with a capacity <strong>of</strong> 25 cc (resolution <strong>of</strong> 0.05 cc) as well as the scale (resolution <strong>of</strong> 1<br />
mm) suctions up to ψ = 4.0 kPa in steps <strong>of</strong> ∆ψ = 0.1 kPa c<strong>an</strong> be applied to the specimen.<br />
The water inflow <strong>an</strong>d the water outflow is measured in the burette during testing procedure.<br />
By adjusting the burette a const<strong>an</strong>t suction is maintained in the specimen when performing<br />
the experiments. The middle part acts as a strengthening <strong>of</strong> the specimen ring <strong>an</strong>d <strong>of</strong>fers a<br />
connection to <strong>an</strong> air pressure system, that acts on top <strong>of</strong> the specimen below the porous stone.<br />
The air pressure system is used to apply suctions up to ψ = 50 kPa to the s<strong>an</strong>d specimen.<br />
The top part <strong>an</strong>d the middle part are separated by a membr<strong>an</strong>e, that includes the porous<br />
stone. Whereas the modified pressure plate is set into a oedometer frame for application <strong>of</strong><br />
vertical net stress in the controlled-suction oedometer <strong>an</strong> air pressure system applies stress<br />
to the membr<strong>an</strong>e from the top <strong>an</strong>d thus vertical stress to the specimen. The bottom part,
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