Hydro-Mechanical Properties of an Unsaturated Frictional Material

90 CHAPTER 4. EXPERIMENTAL SETUPS
Dielectric constant (-)
Dielectric constant (-)
82
81
80
3 79
0
1
2
Deaired water
TDR1 TDR2 TDR3
TDR4 TDR5
Air 0 10 20
Time (min)
30
Time (min) 30 20 10 0
Figure 4.16: Measurement of the dielectric constant of water (top) and air (bottom)
deaired water and the bottom diagram the measurements in the air. As expected the dielec-
tric constant for the deaired water was ka = 1 and for air ka = 80. The measurements also
differ not so much.
Cabral et al. (1999) examined the influence zone around TDR probes and found an influ-
ence zone for the Mini Buribale Waveguides (TDR probes used for this investigation) that is
90 mm in length, 15 mm in height and 35 mm in depth. Sizing of a calibration cell, that can
be used for the determination of the relationship between dielectric constant and volumetric
water content θ(ka) was studied by Suwansawat & Benson (1999). The authors found that
a distance of 36 mm between the cell and the probe as well as a distance of 30 mm between
the probes is required for determination of the calibration function. The calibration cylinder
used in this study is considering the influence zone given by Cabral et al. (1999) and the
distances given by Suwansawat & Benson (1999). For calibration of the TDR probes Hostun
sand samples with predefined volumetric water content and void ratio, were prepared in a