Hydro-Mechanical Properties of an Unsaturated Frictional Material

190 CHAPTER 9. NUMERICAL SIMULATION OF COLUMN TEST BY FEM
Pore-water pressure (Pa)
Pore-water pressure (Pa)
3000
2000
1000
0
-1000
-2000
-3000
-4000
0
-1000
-2000
-3000
-4000
Results simulation
Results experiment
Depth 70 mm
Pore-water pressure (Pa)
Pore-water pressure (Pa)
3000
2000
1000
0
-1000
-2000
-3000
-4000
0
-1000
-2000
-3000
-4000
Results simulation
Results experiment
Depth 160 mm
0 200 400 600 800 1000 1200 1400 1600 0 200 400 600 800 1000 1200 1400 1600
3000
3000
Results simulation
Results simulation
Time (s)
Time (s)
2000
2000
Results experiment
Results experiment
Depth 260 mm
Depth 360 mm
1000
1000
0 200 400 600 800 1000 1200 1400 1600
Time (min)
0 200 400 600 800 1000 1200 1400 1600
Time (min)
Figure 9.4: Comparison of saturation versus time measurements and simulation including
hysteresis model from Parker and Lenhard (1987) - transient state test
- Comparison using soil-water characteristic curve from steady-state experiment:
Due to missing information on either saturation or pressure measurements it is quite
common to use suction-water content parameter set from separately performed tests.
The simulations presented above show that if the soil-water characteristic curve that is
directly measured in the transient state test is used combined with the numerical im-
plementation of the Parker and Lenhard hysteresis concept, a good agreement between
measured and predicted pressure versus time and saturation versus time relationships is
obtained. However, the traditional approach is to measure the drainage and imbibition
suction-water content curves in separate steady-state test (here modified pressure plate
apparatus) and then use this information as input for numerical simulation in order to
obtain predictions on hysteretic unsaturated flow. The classical approach is applied here
and the results are given in Fig. 9.6 and 9.7. While during the transient state tests air
trapping for imbibition process was measured, during steady state test no air trapping
for imbibition process is observed. Therefore it is expected that the soil-water charac-
teristic curve from the steady-state experiment will not provide a good prediction. As
assumed the simulation results show no proper agreement with respect to the entrapped