Environmental Engineering Reference
In-Depth Information
230
High-air-entry disk ports, u w
190
990
450
186
0
2129
min.
S 3 N 3 0
Consolidation
150
110
70
Experiment
(symbols only)
30
Model
(symbols joined by line)
-10
60
65
70
75
80
85
90
95
100
Pore pressures, u (kPa)
(a)
0
1
2
3
4
5
6
7
8
9
10
11
Consolidation
S 3 N 3 0
Total: Experiment
Total: Model
Water: Experiment
Water: Model
0
200
400
600
800
1000
1200
1400
1600
1800
2000 2200
Elapsed time, t (min)
(b)
Figure 16.17 Comparisons between theoretical simulation and experimental data from consoli-
dation test on silty sand (No. S 3 N 3 O): (a) pore-water pressure profiles at different times; (b) total
and water volume changes during consolidation (from Rahardjo, 1990).
Figure 16.18 shows the water phase degree of
consolidation-time factor curves for various air-water inter-
action constants. Similar curves for the air phase are shown
in Fig. 16.19. The interactive constant in the air phase PDE
was assumed to be constant for the calculation of pore-
air pressure dissipation. The curves show a smooth
transition toward the case of a completely saturated soil
(Terzaghi, 1943) and the case of a completely dry soil
(Blight, 1971).
The relationships between these dimensionless numbers
(Figs. 16.18 and 16.19) can be used as a general solution
for one-dimensional consolidation. Appropriate curves
corresponding to the air and water phases can be used
for different coefficient-of-consolidation and soil constant
values.
16.6 COUPLED FORMULATIONS AND
THREE-DIMENSIONAL CONSOLIDATION
One PDE has been used for analyzing water flow with
respect to time and another PDE has been used for analyzing
air flow with respect to time. It is possible to use an iter-
ative process to ensure that both the water phase and air
phase PDEs have converged; however, the total stress equi-
librium equations were not taken into consideration. The
assumption was made that since the total stresses were not
changed during the transient process there was no need
to consider the stress equilibrium equations. This is a rea-
sonable assumption, but the analysis does not constitute a
rigorous formulation and solution of the consolidation pro-
cess in unsaturated soils.
 
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