Environmental Engineering Reference
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35
30
25
a
= 10 kPa; drying curve
20
a
= 7.50 kPa; median curve
15
a
= 5.623 kPa; wetting curve
10
5
0
10
6
0.1
1
10
100
1000
10,000
100,000
Soil suction, kPa
Figure 4.104
Comparison of drying curve, wetting curve, and median curve for soil with lateral
shift of 25% between drying and wetting curves (e.g., sand) and saturated gravimetric water
content of 30%.
45
40
a
= 200 kPa; drying curve
35
a
= 112.5 kPa; median curve
30
25
a
= 63.25 kPa; wetting curve
20
15
10
5
0
10
6
0.1
1
10
100
1000
10,000
100,000
Soil suction, kPa
Figure 4.105
Comparison of drying curve, wetting curve, and median curve for soil with lateral
shift of 50% between drying and wetting curves (e.g., silt) and saturated gravimetric water content
of 40%.
desorption curve provides an estimate of the maximum
value for in situ soil suction. (2) The estimated adsorption
curve provides an estimate of the minimum value for in situ
soil suction. (3) The estimated median curve provides an
estimate closest to the most likely (or middle) in situ soil
suction.
The percent error in the estimated soil suction can be
referenced to the drying curve. Because of the logarithmic
nature of the SWCCs, it is possible for the errors in the
estimated soil suction to be quite large. The potential errors
are much smaller for sand soils than for soils with high clay
content.
The above analysis indicates that it is difficult to obtain
an accurate indication of in situ soil suction through use
of SWCCs and the measured natural water content of the
soil. The proposed procedure merely allows the engineer to
obtain a crude approximation of in situ suction conditions.
The analysis provides a warning to geotechnical engineers
who desire to indiscriminately use the SWCC to estimate in
situ suction. The analysis also provides a guide to engineers
who desire to assess the likely range of in situ suctions
that might correspond to a single water content measure-
ment. Users of the SWCCs should also be aware that in situ
suctions in any soil can range between zero and 10
6
kPa.
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