Geoscience Reference
In-Depth Information
Table 7.18
Soil suction values (Gay and Lytton, 1972; Hillel, 1971).
Soil suction
State
Soil-plant-atmosphere continuum
pF
kPa
1
1
Liquid limit
2
10
Saturation limit of soils in the field
15 kPa for lettuce
3
100
Plastic limit of highly plastic clays
Soil/stem
4
1,000
Wilting point of vegetation (pF
=
4.5)
Stem/leaf: 1500 kPa for citrus trees
5
10,000
Tensile strength of water
Atmosphere; 75% relative
humidity (pF
5.6)
=
6
100,000
Air dry
45% Relative humidity
7
1,000,000
Oven dry
•
Equilibrium moisture condition is related to equilibrium soil suction. Refer to
section 13.
•
Soil suction contributes to strength in the soil. However, this strength cannot be
relied upon in the long term and is often not directly considered in the analysis.
7.19 Soil suction values for different materials
•
The soil suction depends on the existing moisture content of the soil. This soil-
water retention relationship (soil water characteristic curve) does vary depending
on whether a wetting or a drying cycle.
Table 7.19
Typical soil suction values for various soils (Braun and Kruijne, 1994).
Volumetric moisture
Soil suction (pF)
content (%)
Sand
Clay
Peat
0
7.0
7.0
7.0
10
1.8
6.3
5.7
20
1.5
5.6
4.6
30
1.3
4.7
3.6
40
0.0
3.7
3.2
50
2.0
2.8
60
0.0
2.2
70
0.3
- Volumetric moisture content is the ratio of the volume of water to the total
volume.
-
0, as this
is an oven dried condition. Thus for all practical purpose the effect of soil
suction in sands are small.
- Greater soil suction produces greater moisture potential change and possible
movement/swell of the soil.
Soils in its natural state would not experience the soil suction pF
=
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