The Infiltration Numerical Simulation for Several Kinds of Unsaturated Soil under Rainfall Condition - Advanced Research on Computer Education, Simulation and Modeling - page 245

∫

{ Q }

e

{ Q }

e

= − N q d Γ

q is the normal boundary flux on

superposition of , ,

2 2 i 2

, ∫

{ 3 q
is rainfall intensity. If water depth is less than 0, it does not need to calcu-
late

{ Q is the superposition of }

e e

=

Γ

{ Q } Q } N q d S

of runoff element;

3 i

* *

[ A , ] [

B and

] [

B .

]

3 Analysis Model

Based on the couple model, the infiltration processes of a soil column with 8.75cm
width, 8.75cm length and 61 cm height are simulated. The soil columns are silt, silt
clay and clay respectively, which are homogeneous and isotropic. The densities (ρ)
and saturated conductivities (Ks) of soils are listed in Table 1.

Table 1. The parameters of soils

Soil type Silt Silt clay Clay

ρ(g/cm3) 2.00 1.95 1.80

Ks(*10 -2 cm/min) 0.69 0.35 6.9×10-3

The soil-water characteristic curves is described by Fredlund model as eq.(5).

1

S = (5)

e

h

{ln[ e + ( )

n

]}

m

a

The fitness parameters of Fredlund model for four soils are shown in Table 2 [4].

Table 2. Parameters in soil-water characteristic curve

Soil type a(Kpa) n m

Silt 68 1.189 0.796

Silt clay 186 0.594 0.482

Clay 109 0.728 0.556

Suppose the initial volume water content is 0.10, the top boundary is rainfall, and
the other boundary is impervious. The rainfall intensity and duration will be given in
next section.

4 Numerical Simulation Results and Analysis

4.1 Infiltration Process of Silt Column

The rainfall intensity is given as 5.0cm/h, and the rainfall duration is 180minutes.
Calculation results show that the soil suctions decrease rapidly at the beginning, then