Hydro-Mechanical Properties of an Unsaturated Frictional Material

80 CHAPTER 4. EXPERIMENTAL SETUPS
Domain Reflectometry Sensors Time
TDR3 TDR2 TDR1
Tensiometers Dial gauge
T2 T1 Datalogger
PC 1 PC 2 T4 T5 T3 TDR4 TDR5 Multiplexer Trase Water reservior Soil specimen
Cylinder Pump
Figure 4.4: Set up of column testing device I
the plexiglas plate as well as between the plexiglas plate and the water reservoir sealing rings
are placed to ensure leakproof connection. A highly permeable geotextile is placed between
the soil specimen and the perforated plexiglas plate to avoid flushing soil grains to the water
reservoir. Several openings (6 openings on one side and 5 openings on the opposite side) along
the column enable to connect sensors to the column.
Five miniature tensiometers (UMS Umweltanalytische Mess-Systeme GmbH) and 5 minia-
ture Time Domain Reflectometry probes (Soil Moisture Equipment Corp.) are placed in a row
along the height of the column in a distance of about 100 mm between measurement points.
The tensiometers are pressure transducer tensiometers which are horizontally installed into
the soil specimen. The TDRs are three rode sensors, which are also horizontally installed into
the soil specimen. One couple of TDR sensor and tensiometer sensor is installed at the same
height. This procedure allows directly to link suction to the volumetric water content in the
soil in different layers during drainage and imbibition of the specimen.
An electronic pump is connected to the reservoir at the bottom of the column to facilitate
the injection and withdrawing of water at a constant rate. In this study a membrane pump
of type KNF FM 15KT18 (LAT Labor- und Analysentechnik GmbH) was used. By changing
the stroke of the membrane, the flow rate can be changed from 10 to 150 ml/min. The motor
of the pump has a constant speed of 75 revolutions per minute. Thus the pump is able to
withstand 6 bar back-pressure and the flow rate is not depending on a hydraulic head up to
6 bar back-pressure. Because in the transient state test a constant flow rate is applied to
the soil specimen, it was carefully checked that the flow rate is constant (see Fig. 4.6). The
diagram shows that there is no influence of the hydraulic head on the flow rate. The flow
rate is constant. Atmospheric pressure was acting at the top of the column. Volume changes