Consolidation and Swelling Processes in Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 848

Distance from center of cover (m)

0 2 4 6 8 10 12

Flexible slab

− 22

Rigid slab with small gap

Rigid slab with no gap

− 27

Day 5

− 32

Figure 16.55 Comparison of vertical displacement profiles when using flexible slab, rigid slab
with no gap, and rigid slab with a small gap.

1000

100 q = 10 mm/day

q = 20

10

Edge of
slab

q = 40
q = 60

1

0.1

0.01

0.001

e m = 1.9 m

0.0001

1 2 3 4 5 6 7

Distance from center of slab (m)

Figure 16.56 Suggested approach to estimation of edge moisture distance e m .

from a plot of the vertical displacement along the ground
surface.
The edge-drop case can also be modeled through use of a
“no-tension” finite element at the interface between the soil
and the underside of the concrete slab. The edge moisture
variation distance e m can still be defined in terms of the
distance from the edge of the concrete slab to the point
where the contact vertical stresses become positive.
The above example is simply meant to illustrate how prob-
lems associated with edge drop might be analyzed using a
combined seepage and stress-deformation numerical model.

and the concrete slab. Further studies should be undertaken
into how best to use the climatic conditions in a particular
region to obtain appropriate design conditions for slabs-on-
ground.

16.10 THEORY FOR SIMULATION OF SWELLING
PRESSURE DEVELOPMENT

The development of swelling pressure in laboratory testing is
another example of the application of combined seepage and
stress-deformation analyses in unsaturated soil mechanics.
Numerous methods have been proposed for the prediction
of the swelling pressure and the amount of heave of an
expansive soil. However, there have been few attempts to
numerically simulate the swelling process and the develop-
ment of the swelling pressure. Complicating the swelling
pressure simulation is the variety of different stress paths
used in the laboratory to measure swelling pressure.
The swelling pressure measured in the laboratory may dif-
fer significantly depending on the test procedure used for its

16.9.4 Methodology for Modeling Edge-Rise Case
The edge rise case occurs when the soil beneath the edge
of the concrete slab swells as a result of moisture infiltration.
There may once again be a loss of contact beneath the soil and
the bottom of the concrete slab. The zone over which there is
a loss of contact will depend upon the pattern of swelling in
the underlying soil. The use of a no-tension element can once
again be used when modeling the interface between the soil