Environmental Engineering Reference
In-Depth Information
+
0.4
0.2
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Air phase
-
Water phase
1.8
Coefficient of permeability of :
Water: 1.0 x 10
Soil structure
10
2.0
m/s
2.2
13
Air: 8.0 x 10
m/s
2.4
1
10
100
1000
10,000
100,000
Elapsed time (min)
Figure 16.9 Theoretical simulation of consolidation test on unsat-
urated compacted kaolin (test 1).
Figure 16.8 Soil structure and water phase volume changes asso-
ciated with increase in water pressure (test 5).
Eqs. 16.3 and 16.4. The coefficients of volume change used
in the calculations were assumed to be constant throughout
the process. The soil structure volume change was obtained
by adding the volume changes associated with the water and
air phases.
Figures 16.9-16.13 show the results of the theoretical sim-
ulation of tests 1-5. The fitting was accomplished by using
various combinations for the coefficients of permeability for
the water and air phases. The combinations of constant values
for the water and air coefficients of permeability that gave the
best-fit results for each test are shown in each figure. Compar-
isons between the numerical simulations and the laboratory
results weremade for tests 4 and 3 (i.e., Figs. 16.14 and 16.15).
The results indicate reasonably close agreement between the
numerical simulations and the laboratory test results.
Some discrepancies were observed in the simulation of the
transient processes. The disagreements may be due to one
or more reasons. For example, the assumption was made
that the coefficients of permeability were constant through-
out each process. In general, the numerical simulations and
the laboratory results show the anticipated volume change
behavior with elapsed time.
The coefficients of volume change for each phase were
obtained by dividing the amount of deformation at the end
of each process by the change in the stress state variable.
A sign (i.e., positive or negative) is attached to each of the
coefficients of volume change based on the direction of the
volume change (i.e., increase or decrease) associated with
each phase and the change in the stress state variables.
Table 16.3 indicates that the coefficients of volume change
for the soil structure have negative signs for a stable-
structured soil (i.e., tests 1, 2, and 4) and positive signs for
a metastable-structured soil (i.e., tests 3 and 5). A negative
coefficient of volume change suggests there is an increase in
volume for a decrease in the stress state variable, while a
positive coefficient of volume change indicates the converse.
The theoretical simulation of the laboratory results was
performed by assuming one-dimensional transient flow pro-
cesses. The pore-water and pore-air pressure equations (i.e.,
Eqs. 16.40 and 16.42) can be solved simultaneously using
an explicit central finite difference technique. The coeffi-
cients of permeability for air and water were assumed to be
constant during the transient process.
The volume changes associated with the water and air
phases during a transient process were computed using
16.4.4 Tests on Silty Sand
One-dimensional consolidation tests were conducted on silty
sand using a special K 0 cylinder designed by Rahardjo (1990).
Table 16.3 Coefficients of Volume Change for Each Specimen
Soil Structure
Water Phase
Air Phase
m 1 ×
10 4 kPa 1
m 2 ×
10 4 kPa 1
10 4 kPa 1
10 4 kPa 1
m 1
10 4 kPa 1
m 2
10 4 kPa 1
m 1
m 2
Tes t No.
×
×
×
×
1
1.17
3.52
0.80
2.41
0.37
1.11
2
0.006
0.032
0.131
0.657
+
0.125
+
0.625
3
+
0.76
+
3.80
0.30
1.49
+
1.06
+
5.29
4
0.09
0.35
0.15
0.61
+
0.06
+
0.26
5
+
0.26
+
1.04
1.20
4.81
+
1.46
+
5.85
 
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