Hydro-Mechanical Properties of an Unsaturated Frictional Material

7.2. SOIL-WATER CHARACTERISTIC CURVE 149
7.2.4 Comparison of Steady State and Transient State Results
For investigation of the influence of flow condition on the shape of the soil-water characteristic
curve, steady state tests were performed in the modified pressure plate apparatus and also in
the sand column testing device I. Transient state tests were performed in sand column test
I, where 2 different flow rates were applied to the sand specimen and in sand column test
II, where air pressure was applied to the top of the sand specimen. Steady state as well as
transient state drainage curves results are shown in Fig. 7.9. Neither for the loose specimens
nor for the dense specimens significant influence of flow condition on the shape of the soil-
water characteristic curve was observed. Soil-water characteristic curve parameters derived
from all experiments are summarized in Tab. 7.1 for loose and dense specimens. Values as
the air-entry value or the residual suction are in the same range for each the loose as well
as dense specimens. Thus the dynamic effect is not influencing the shape of the soil-water
characteristic curve for the investigated material. The drainage soil-water characteristic curve
Volumetric water content (%)
Volumetric water content (%)
50
40
30
20
10
0
50
40
30
20
10
0
press. plate app. - steady state Sand col. test I - transient state, 30 ml/min Sand col. test I - transient Mod.
0 2 4 6
Suction
state, 100 ml/min Sand col. test I - steady state Sand col. test II - transient state, 3.5 kPa air-pressure
(kPa)
specimen Initial void ration = 0.89 Loose
Dense specimen
0 2 4
Suction (kPa)
6
Initial void ration = 0.66
Figure 7.9: Influence of flow condition (steady state, transient state flow) on the shape of the
soil-water characteristic curve