Hydro-Mechanical Properties of an Unsaturated Frictional Material

30 CHAPTER 2. STATE OF THE ART
Table 2.2: Overview of equipment for determination of the soil-water characteristic curve
Equipment Technique Type Range (10 3 kPa)
Tempe pressure cell Axis-translation Matric suction 0...1.5
Pressure Plate Apparatus Axis-translation Matric suction 0...1.5
Thermal Conductivity Sensor - Matric suction 0.01...1
Thermocouple Psychrometer Humidity Total suction 0.01...8
measurement
Chilled Mirror Hygrometer Humidity Total suction 1...450
measurement
Filter Paper - Total or Matric 0...1000
suction
in the soil specimen (Eching & Hopmans 1993, Eching et al. 1994, Wildenschild et al.
2001, Fujimaki & Inoue 2003). Consequently the hydraulic properties of the porous
medium can be determined based on the applied/ measured pressure and water mass
data.
- One-step Method:
The one-step flow method is a transient state test and was first proposed by Gard-
ner (1956). During the testing procedure a specimen is placed in a cell with a porous
plate at the bottom. After the saturation process pressure is applied from the upper
compartment of the cell. The resulting outflow of the fluid is measured as a function
of time. One-step flow experiments were performed by Topp et al. (1967), Kool et al.
(1985b), Dam et al. (1992), Toorman & Wierenga (1992), Wildenschild et al. (1997,
2001), Schultze et al. (1997). The authors carried out the one-step method experi-
ments either in tempe cells, pressure cell apparatus (Kool et al. 1985b, Dam et al. 1992,
1994) or modified pressure cells (Toorman & Wierenga 1992, Eching & Hopmans 1993,
Wildenschild et al. 1997, 2001). Wildenschild et al. (1997, 2001) used their modified
pressure cell also to induce a continuous outflow scenario at a constant flow rate using
an attached syringe pump.
- Continuous Flow Experiments:
Continuous flow experiments, that are for instance evaporations tests, gravity drainage
tests or test where a flow rate is applied to the soil, are performed in large column appa-
ratuses. Conventional column apparatuses are equipped with sensors (e.g. tensiometer
sensors, TDR sensors) for measuring the soil-water characteristic curve while draining
and wetting the soil and usually the soil is placed on a porous stone (Schultze et al.
1997). In many studies only pore water pressure measurements (Chapius et al. 2007)
are performed and therefore inverse procedure has to be used to determine unsaturated
soil parameters. Nützmann et al. (1998) used a column apparatus for determining hy-