Actes du colloque - Volume 2 - page 325

1196
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
0 10 20 30 40 50
0
1
2
3
4
5
6
t(sec)
Depth of saturation front from ground surface (cm)
Sand Sandy loam Clay loam Silt
Figure 2. Depth of saturation front as a function of time.
0
10
20
30
40
0
10
20
30
40
Sturated front
Wetting front
t(sec)
Depths of both of front
(cm)
Figure 3. Observed depth of saturation front and wetting front as a
function of time.
The numerical simulations showed that the depth of a
saturation front was proportional to the square root of time
when a constant water level of 10 cm was applied. It is
considered that nonlinearity arouse in the second half of the
experiment due to the presence of silt. Fig. 3 shows the
experimental results obtained when water moving through sand
was observed using four-point moisture sensors. Since the time
of onset of watering is not clear, there is a gap in the range and
time, but the results obtained by numerical simulation and in the
experiments produced the same results.
These data show that shows that we can determine the depth
of a saturation front using one proportionality factor and the
following equation:
t s H
s
(1)
where,
H
s
is the depth of saturation front,
t
is elapsed time and
s
is the regression parameter.
3 OUTLINE OF PERMEATION TEST
3.1
Experimental apparatus and measured parameters
A soil chamber was used to imitate the experimental apparatus
in-situ (Fig. 5). As shown in Fig. 4, the main part of the
experimental apparatus has a Marriott tank and a circular water
supply part. The circular water part is inserted into the
foundation and a perpendicular flow is maintained. The
tensiometer which measures pore pressure was installed at a
depth of 50 mm in the centre of the water supply part. In order
to obtain a constant pressure with the water supply part, the
difference in the hydraulic head was set to 100 mm using the
Marriott tank.
Figure 4. Experimental apparatus used for permeation test.
Figure 5. Setting for apparatus for permeation test.
3.2
Calculation of saturated hydraulic conductivity
Dry Toyoura sand was used for the permeation experiment, the
results of which are shown in Fig. 6. When the pressure head
becomes fixed at a depth of 50 mm, it turns out that the amount
of infiltration is also fixed. When an observed pressure head
maintained the same, it is judged that the point of 50mm in
depth was saturated. Moreover, a hydraulic gradient can be
estimated by subtracting the difference between the pressure
head of the earth surface under the he circular water part, and
the pressure head observed in the ground. The saturated
coefficient of permeability became 1.0E-4 m/s when the incline
of the accumulation amount of infiltration became a constant.
0
50
100
150
-40
-30
-20
-10
0
10
20
0
500
1000
Elapsed time (sec)
Pressure head |h
p
| (cm)
Accumulated amount of
infiltration (cm
3
)
Pressure head at depth of 5cm
Pressure head at ground surface
Accumulated amount of infiltration
h
p
Incline is constant.
Figure 6. Measure values for permeation test
4 ESTIMATED MOISTURE DISTRIBUTION
4.1
Linear approximation of the soil water distribution
In order to calculate the hydraulic conductivity of unsaturated
ground, information on the degree of saturation is required. In
particular, in conditions of unsteady flow, since the amount of
moisture changes with depth, it is necessary to accurately
determine the distribution of moisture over time.
The authors therefore assumed a moisture distribution changes
over time using the relation between Fig. 1 and Eq. 1. It is
assumed that any infiltration assumes a trapezoidal distribution
consisting of two components; the depth of the saturation front
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