Hydro-Mechanical Properties of an Unsaturated Frictional Material

120 CHAPTER 6. EXPERIMENTAL RESULTS
Volumetric water content (%)
Saturation (-)
50
40
30
20
10
0
Volumetric water content (%)
TDR/T260 mm - drainage TDR/T 260 mm - imbibition
0.1 1 10 100 0.1 1 10 100
1.0
Suction (kPa)
1.0
Suction (kPa)
0.8
0.6
0.4
0.2
0.0
70 mm - drainage TDR/T 70 mm - imbibition TDR/T 160 mm - drainage TDR/T 160 mm - imbibition TDR/T
Saturation (-)
0.1 1 10 100
Suction (kPa)
specimen Initial void ratio = 0.88 Loose
50
40
30
20
10
0
0.8
0.6
0.4
0.2
0.0
70 mm Depth 260 mm TDR Depth 160 mmTensiometer
0.1 1 10 100
Suction
Dense specimen
(kPa)
void ratio = 0.67 Initial
Figure 6.5: Readings from tensiometers and TDR sensors linked to drainage and imbibition
soil-water characteristic curves from steady state column test I (loose and dense specimen)
soil-water characteristic curve. Similar to the measurements observed in the modified pressure
plate apparatus, the experimental results measured in the sand column testing device I show
the effect of hysteresis. Between main drainage and imbibition loop several scanning drainage
and imbibition curves were found in the modified pressure plate test results. Comparing the
hysteresis of the volumetric water content-suction curves the loose specimen enclose a larger
area than the dense specimen. The effect of occluded air bubbles was found to be significant
for the results derived from the sand column I tests, particularly for the loose specimen.
6.2.2 Transient State Test Results
Suction measurements were performed in several depth during experiments carried out in sand
column device I under transient state condition using tensiometer sensors (Fig. 6.6). These
measurements were carried out parallel to volumetric water content measurements using TDR
sensors that are also presented below (Fig. 6.7). The results are pairs of tensiometer and TDR
readings, which are linked to the soil-water characteristic curve (Fig. 6.8).
Typical tensiometer results measured in transient state column test I are given in Fig. 6.6.
These figures respectively show the measurements derived from the drainage and imbibition
processes observed from both the loose and dense specimen. As described in the laboratory