Consolidation and Swelling Processes in Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 851

2.5

s = 4.0 x 10 −

10 m/s
s = 4.0 x 10 − 11 m/s
s = 4.0 x 10 −

k
k
k

2.0

12 m/s

1.5

1.0

0.5

0.0

0.1 1 10 100 1000 10,000 100,000

Matric suction ( u a - u w ) (kPa)

Figure 16.61 Computed swelling rates in free-swell oedometer test using different saturated
coefficients of permeability.

300

200

100

Access to water from bottom
Access to water from bottom and top

0

0.1 1 10 100 1000 10,000

Time ( t ) (min)

Figure 16.62 Time rate for development of swelling pressure depending on length of
drainage path.

from the surface of a soil specimen placed in an oedometer
was investigated using the proposed free-swell model. A
20-mm-thick soil specimen was assumed to have a surface
water loss due to evaporation at a rate of 2

at the surface of the soil specimen at the end of the test has
decreased to about 15 kPa.

10 − 8 m/s (i.e.,
1.72 mm/day). The computed deflection versus elapsed time
curves presented in Fig. 16.63 show that the evaporation of
water from the surface of the soil significantly reduced the
total heave and the rate of swelling in a free-swell test.
The computed matric suction profiles are presented in
Fig. 16.64. The initial matric suction throughout the soil
specimen was 600 kPa. The computed results show that
matric suction increases due to moisture loss due to evap-
oration during early stages of the test. The volume of the
soil specimen decreases in the upper part of the specimen.
The matric suction at the surface reaches 2600 kPa after
120min of swelling and then decreases. The matric suction

×

16.11 RHEOLOGICAL MODEL
FOR UNSATURATED SOILS

Rheological models can serve an important role in visual-
izing the physical processes associated with consolidation
and swelling. The Kelvin model, for example, proved to
be useful in communicating the time-dependent response of
a saturated soil to an applied load. The instantaneous and
time-dependent processes of an unsaturated soil are more
complex than those of a saturated soil and it is important to
be able to visualize unsaturated soil behavior. The proposed
rheological model for an unsaturated soil might never be
used to solve practical geotechnical engineering problems;