Theory of Water Flow through Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 364

Table 7.9 Moisture Flux Conditions Applied to Slope Models

Rainfall Evaporation

Name of Name of Intensity Duration Mode of Measured Potential Duration

Model Test (mm/h) (mm/h) Evaporation Evaporation (mm/h) (h)

SM1 SM1 T1 8.95 3 Ambient condition 0.02 475

SM1 T2 9.01 3 Lamp 0.20 120

SM1 T3 8.88 3 Fan 0.12 120

SM1 T4 9.04 3 Lamp and fan 0.22 80

SM1 SM2 T1 9.68 3 Lamp and fan 0.43 100

SM2 T2 10.09 3 Ambient condition 0.02 120

SM2 T3 9.88 3 Lamp 0.19 120

SM2 T4 9.85 6 Lamp and fan 0.52 120

used in the slope models. The instantaneous profile method
was used to obtain the permeability function during dry-
ing processes. Water flowed upward from the bottom of
the upper layers during the drying process. Pore-water pres-
sure data from tensiometers T-23, T-24, T-33, T-34, T-43,
and T-44 (see Fig. 7.38) were used for the calculation of
the drying permeability functions. Volumetric water con-
tents were computed based on the SWCC and measured
pore-water pressures (Fig. 7.39). Table 7.8 summarizes the
unsaturated soil parameters used for the calculation of unsat-
urated coefficient of permeability by the instantaneous pro-
file method. The unsaturated coefficients of permeability k w
of RS and MRF 60-40 were plotted against corresponding
matric suctions and are shown in Figs. 7.40 and 7.41.

The unsaturated coefficient-of-permeability functions were
also computed using a statistical estimation method described
by Childs and Collis-George (1950). The calculation of the
permeability function requires the saturated coefficient of
permeability and SWCC. The saturated coefficient of perme-
ability of the RS was 9 10 − 7 m/s. The MRF 60-40 soil had

a saturated coefficient of permeability of 5

×

10 − 6 m/s. These
values appear to be about one order of magnitude higher than
the saturated coefficient of permeability obtained from the
independent falling-head tests (Table 7.7).
The instantaneous profile method and the statistical esti-
mation method were used to obtain permeability functions
for the RS and the MRF 60-40, comprising the slope mod-
els. The estimated permeability functions appeared to pro-
vide a reasonable representation of the actual permeability

×

-7

T-24

t = 4 d

-6

-5

-4

t = 3 d

-3

T-23

t = 2 d

-2

-1

t = 1 d

0

0.00 0.05 0.10 0.15 0.20

Depth ( z ), m

Datum, z = 0

Figure 7.38 Hydraulic head profiles for Test SM1-T1 measured by tensiometers T-23 and T-24
during drying process (after Krisdani et al., 2009).