Environmental Engineering Reference
In-Depth Information
pressure needed to keep the pollutant saturation equal to 0.5 and is obtained from
the
p
c
−
S
w
relation. The vertical displacements are free on the top surface. The
initial conditions assume zero displacements for the solid and fluid pressure equal to
the reference one.
The results shown in Figure 14.12 indicate the influence of the permeability of
the medium on the saturation and vertical displacements.
Figure 14.12.
Vertical displacements and saturation profiles within the column
for two values of intrinsic permeability: continuous line k = 1 x 10
-11
m
2
;
and dashed line k = 1.5 x1 0
-12
m
2
14.3.5.3.
Solute transport in water and air
In this example we analyze moisture and heat flow due to environmental
changes in a 10 cm thick partially saturated soil layer. Convective/diffusive
pollutant transport is coupled with mass transfer. The physical problem could be that
of a soil layer below a highway or airfield runway. The soil is assumed to be in an
equilibrium state initially. Then sudden evaporation or infiltration and temperature
change takes place at the surface. The problem was solved first by [DAK 81] with a
rather simplified model compared to that used here: in [DAK 81] the permeability
was constant, the soil rigid and the effects of temperature gradients on the mass
transfer neglected.
In the solution shown [ZHA 95] the relationships between relative permeability,
saturation and capillary pressure proposed by [BRO 66] are used. Solute transport in
both fluid phases is considered. The problem is modeled with equation system
[14.21]. A column of 10 square finite elements of equal size over thickness is
adopted. Nine-node elements are used, each node having seven degrees of freedom.
The temporal discretization of equation system [14.21] is fully implicit.
