Hydro-Mechanical Properties of an Unsaturated Frictional Material

126 CHAPTER 6. EXPERIMENTAL RESULTS
Pore-water pressure (kPa)
2
1
0
-1
-2
-3
-4
Loose specimen
Initial void ratio = 0.89
Pore-water pressure (kPa)
0 1000 2000 3000
Time (min)
2
1
0
-1
-2
-3
-4
Dense specimen
Initial void ratio = 0.66
0 1000 2000 3000
Time (min)
T - top
T - middle
T - bottom
Figure 6.9: Suction measurements for drainage process from transient state column test II
(loose specimen-left, dense specimen-right)
Volumetric water content (%)
50
40
30
20
10
0
Volumetric water content (%)
0 1000 2000 3000
Time (min)
Loose specimen
Initial void ratio = 0.89
50
40
30
20
10
0
0 1000 2000 3000
Time (min)
Dense specimen
Initial void ratio = 0.66
TDR - top
TDR - middle
TDR - bottom
Figure 6.10: Volumetric water content measurements for drainage process from transient state
column test II (loose specimen-left, dense specimen-right)
Figs. 6.12 for both loose and dense specimen. Since the initial condition is equal in each
measurement depth (initially saturated specimen), the shape of the measured soil-water char-
acteristic curve is similar.
As the steady state test results, the transient state results show an influence of void ratio
on the shape of the soil-water characteristic curve, that will result in different soil-water
characteristic curve parameters as for instance air-entry value, residual suction and water-
entry value for loose and dense specimen. The measurements derived during drainage and
imbibition process are not unique that leads to the phenomena of hysteresis. In sand column
test I experiments several scanning imbibition curves were found. Even after several performed
imbibition processes in sand column I tests a fully saturated specimen was not achieved again.
Here also the effect of occluded air bubbles was found to be significant for both the loose and