Environmental Engineering Reference
In-Depth Information
Table 16.4 Initial Soil Properties and Stress State
Variables for S1FG Consolidation Test on Silty Sand
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0.2
0.4
Theory
Experimental data
Water phase
Initial Volume-Mass
Properties
S
98.0 %
+
e
0.578
Soil structure
w
21.2 %
-
n
0.366
0.1
1.0
10
100
1000
10,000
Elapsed time (min)
Stress State Variables (kPa)
σ
184.3
Figure 16.14
Comparisons between theoretical simulation and
laboratory test data for test 4 with increase in water pressure.
u
a
(top)
119.5
u
w
(bottom)
106.7
σ
−
u
a
64.8
4
u
a
−
u
w
12.8
Theory
Experimental data
3
2
+
1
Water phase
0
1
2
3
4
5
6
7
-
numerical simulation of consolidation and the experimental
results, as demonstrated in Fig. 16.17a.
The total water volume changes during the consolidation
process (i.e., Fig. 16.17b) are similar to those presented in
Fig. 16.16b. The net normal stress remained constant during
the consolidation process following constant-water-content
loading while the matric suction increased due to the dissi-
pation of the excess pore-water pressures. The total volume
change and water volume change were simulated using Eqs.
16.2 and 16.3, respectively. The best-fit coefficients of vol-
ume change were found to be 8
Soil structure
0.1
1.0
10
100
1000
10,000
Elapsed time (min)
Figure 16.15
Comparisons between theoretical simulation and
laboratory test data for test 3 with decrease in air pressure.
10
−
5
kPa
−
1
for
m
2
and
m
2
, respectively. The above examples verify the
unsaturated soil theory of consolidation.
10
−
6
and 3
.
8
×
×
manner (i.e., a transient process), as demonstrated in
Fig. 16.16a. The water volume change (i.e., 10.5 cm
3
),
exceeded the time-dependent total volume change (i.e.,
6.0 cm
3
), as shown in Fig. 16.16b. However, the soil
structure underwent an immediate volume decrease of
9.0 cm
3
during the undrained loading prior to pore pressure
dissipation. The immediate volume change was caused by
compression of the soil structure and the air. The overall
volume change was larger than the water volume change in
response to an increase in total stress.
Another set of results from a consolidation test on the
silty sand is presented in Fig. 16.17. The total stress was
increased under constant-water-content conditions prior to
consolidation. As a result, only excess pore-water pressures
were developed during loading. The excess pore-water pres-
sure dissipation during the consolidation process is shown
in Fig. 16.17a for various depth and time intervals. The
pore-water pressure isochrones were best fitted with the
transient water flow equation. There was no measurable
air flow during the transient process. The coefficients of
permeability and volume change for the water phase were
assumed to be constant during the consolidation process.
The best-fit constant coefficient of consolidation
c
v
was
1
.
2
16.5 DIMENSIONLESS CONSOLIDATION
PARAMETERS
The simultaneous solution of the pore-water and pore-air
PDEs (i.e., Eqs. 16.17 and 16.36) can be generalized in
terms of dimensionless numbers similar to those used for
saturated soils. The dimensionless numbers are the average
degree of consolidation and the time factor for the water
and air phases. The average degree of consolidation for the
water phase is defined as
2
d
u
w
dy
0
U
w
=
1
−
(16.43)
2
d
u
w
0
dy
0
where:
U
w
=
average degree of consolidation with respect to the
water phase,
10
−
6
m
2
/s. There was good agreement between the
×
u
w
0
=
initial pore-water pressure,
Search WWH ::
Custom Search