Environmental Engineering Reference
In-Depth Information
Distance from center of cover (m)
0
2
4
6
8
10
12
0
Flexible slab
Concrete slab:
E
= 100 GPa
−
5
−
10
Day 1
−
15
−
20
Day 3
Δ
Flexible slab
−
25
−
30
Day 5
−
35
−
40
Figure 16.53
Comparison of vertical displacement at ground surface for edge-drop case con-
sidering flexible slab and stiffened concrete slab with elastic modulus
E
c
of 100 GPa.
Table 16.11 Differential Deflection for Edge-Drop
Example Considering a Flexible Slab Cover and
Concrete Slab for Varying Elastic Modulus Values
e
m
(also referred to as the edge penetration distance) and
(ii) vertical differential soil movement
y
m
. These variables
are used for the design of a concrete slab-on-ground.
The edge moisture variation distance
e
m
is defined as the
distance measured inward from the edge of the slab of a
shallow foundation where the water content of the soil varies
due to drying and wetting influences around the perimeter.
The selection of the
e
m
distance requires, in essence, the
point where changes in matric suction becomes negligible
or more accurately the point where the volume change of
the soil becomes insignificant.
It is suggested that the edge moisture distance might be
defined using a plot of the change in matric suction versus
the horizontal distance from the edge of the concrete slab,
as shown in Fig. 16.56. The change in matric suction imme-
diately below the concrete slab is plotted on a logarithmic
scale. A threshold value of matric suction change might be
used to estimate the moisture variation distance
e
m
. There
are other possible criteria that might also be used for the
selection of the edge moisture variation distance.
The differential soil movement
y
m
is defined as the
maximum vertical differential soil movement that is likely
to occur. The vertical distance
y
m
might be determined
Day 1
Day 3
Day 5
Elastic
Deflection
Deflection
Deflection
Modulus
(mm)
(mm)
(mm)
Flexible cover
2.09
3.87
5.33
20MPa
1.80
3.55
4.94
10 GPa
1.50
3.48
5.10
100 GPa
1.29
3.16
4.27
made concerning the interaction between the soil and the
underside of the concrete. The deformed shapes can be used
to calculate moments and stresses in the concrete slab.
16.9.3 Interpretation of Edge Moisture Variation
Distance
e
m
and Differential Soil Movement
y
m
There are two variables that play a primary role in the design
of slabs-on-ground: (i) horizontal moisture variation distance
Separation length = 0.6 m
Slab
Separation width = 0.01 m
Soil
Figure 16.54
Modeling separation of concrete slab and expansive soil under soil-drying
conditions.
Search WWH ::
Custom Search