Environmental Engineering Reference
In-Depth Information
1E-04
1E-05
1E-06
1E-07
1E-08
1E-09
1E-10
1E-11
1E-12
1E-13
1E-14
1E-15
1E-16
1E-17
Experimental data
Fredlund and Xing (1997)
Vapor permeability
0.1
1
10
100
1000
10,000
100,000
10 6
Soil suction, kPa
Figure 8.30 Variations of liquid water and vapor permeability function for a silty sand soil.
40
30
20
10
Hysteresis
0
10 6
0.1
1
10
100
1000
10,000
100,000
Soil suction, kPa
8
4
2
Hysteresis
0
10 6
0.1
1
10
100
1000
10,000
100,000
Soil suction, kPa
Figure 8.31 Relationship of water storage functions to drying and wetting SWCCs.
The solution of saturated-unsaturated seepage problems
is presented through a series of problems that are progres-
sively more complex. The first seepage problems are of
a steady-state nature and these are followed by several
unsteady-state (or transient) analysis problems. One-
dimensional steady-state problems are first solved and
these are followed by two-dimensional examples. The one-
dimensional seepage examples illustrate the application
of hydraulic head and moisture flux boundary conditions.
The one-dimensional problems are solved using a finite
difference technique. Two-dimensional steady-state example
problems are then solved using the finite element method.
These example problems are followed by a series of
two-dimensional, unsteady-state examples that are solved
using the finite element methodology.
8.3.1 Solution of One-Dimensional Flow Problems
The differential equation for one-dimensional steady-state
flow through a homogeneous , saturated soil can be solved
by integrating the differential equation two times. The
equation for one-dimensional steady-state flow through an
unsaturated soil requires a more complex solution than that
for a saturated soil. A numerical solution must be used rather
than a closed-form solution. The finite difference method
 
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