Hydro-Mechanical Properties of an Unsaturated Frictional Material

148
CHAPTER 7. ANALYSIS AND INTERPRETATION OF THE EXPERIMENTAL
RESULTS
Influence of flow condition
The drainage curves derived from transient state tests, that were performed under several
flow conditions are shown in Fig. 7.8. For better view the plots are not given in logarithm
form. Even a slow flow rate of 30 ml/min, a fast flow rate of 100 ml/min and air pressure
ua = 3.5 kPa were induced to the sand specimen no significant change or shift of the soil-water
characteristic curve for both the loose and dense specimen was observed. It seems that the
soil-water characteristic curve parameters (the parameter of the saturated volumetric water
content is not taken into account due to presence of occluded air) are similar for drainage
curves performed with a flow rate ≈ 30 ml/min, with a flow rate ≈ 100 ml/min and under
applied air pressure ua = 3.5 kPa. The so called dynamic effect was not found to be significant
for Hostun sand.
Imbibition curves were also performed under several flow conditions (30 ml/min and
100 ml/min), but can not be compared due to different initial condition when starting the
imbibition process.
Volumetric water content (%)
Volumetric water content (%) Loose
50
40
30
20
10
0
50
40
30
20
10
0
col. test I - transient state, 30 ml/min Sand col. test I - transient state, 100 ml/min Sand
0 2 4 6
Suction
Sand col. test II - transient state, 3.5 kPa air-pressure
(kPa) Initial void ration = 0.89 specimen
Dense specimen
0 2 4
Suction (kPa)
6
void ration = 0.66
Figure 7.8: Influence of flow condition on the shape of the soil-water characteristic curve
Initial