Page 260 - Geotechnical Engineering Soil and Foundation Principles and Practice

Soil Consistency and Engineering Classification
Soil Consistency and Engineering Classification 255

Figure 12.6
Data suggesting a
modification to
eq. (12.3) for silty
soil.

the U.S. Bureau of Reclamation. Denisov argued that if the moisture content
upon saturation exceeds the liquid limit, the soil should be collapsible—that is,
it should collapse and densify under its own weight if it ever becomes saturated.
The most common collapsible soil is loess, which is a widespread surficial deposit
in the U.S., Europe, and Asia. Because loess increases in density with depth
and with distance from a source, only the upper material close to a source may be
collapsible, so this is a valuable test.

12.7.2 Moisture Content Upon Saturation

The soil unit weight and specific gravity of the soil mineral grains are required
to calculate the moisture content upon saturation, which are entered into the
following equations:
SI: w s ¼ 100 9:807=
d 1=Gð Þ ð12:5Þ

English: w s ¼ 100 62:4=
d 1=Gð Þ ð12:5aÞ
where w s is the percent moisture at saturation,
d is the dry unit weight in kN/m 3
3
or lb/ft , and G is the specific gravity of the soil minerals. Solutions of this
equation with G ¼ 2.70 are shown in Fig. 12.7.

12.8 CONSISTENCY LIMITS AND EXPANSIVE SOILS

12.8.1 Measuring Expandability

Expandability can be determined with a consolidometer, which is a device that was
developed to measure compression of soil but also can be used to measure
expansion under different applied loads. Samples are confined between porous
ceramic plates, loaded vertically, wet with water, and the amount of expansion
measured. An abbreviated test measures expansion under only applied pressures
that can simulate a floor or a foundation load.

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