Page 281 - Geotechnical Engineering Soil and Foundation Principles and Practice

Soil Consistency and Engineering Classification
276 Geotechnical Engineering

that is lightly greased on the inside and struck off even with the top of the dish,
which has a known weight and volume. The soil then is oven-dried at 1108C and
the weight recorded. The soil pat then is removed and suspended by a thread in
melted wax, drained and allowed to cool, and re-weighed.

During oven-drying the volumetric shrinkage equals the volume of water lost until
the soil grains come into contact, which is defined as the shrinkage limit. Then,

V V d
SL ¼ w 100 ð12:7Þ
m s
where w and V are the soil moisture content and volume prior to drying, V d is the
volume of the pat after oven-drying, and m s is the mass of the dry soil in grams.
The determination assumes that the density of water that is lost during drying is
3
1.0 g/cm .
A so-called ‘‘shrinkage ratio’’ equals the dry density of the soil at the shrinkage
limit:
SR ¼ m s =V d ð12:8Þ
where SR is the shrinkage ratio and other symbols are as indicated above.

12.14.3 COLE

The ‘‘coefficient of linear extensibility’’ (COLE) test is used by soil scientists to
characterize soil expandability, and has an advantage over the shrinkage limit test
in that the original soil structure is retained, which as previously discussed can
greatly reduce the amount of soil expandability. No external surcharge load is
applied. A soil clod is coated with plastic that acts as a waterproof membrane but
is permeable to water vapor. The clod then is subjected to a standardized moisture
tension of 1/3 bar, and after equilibration its volume is determined by weighing
when immersed in water. The volume measurement then is repeated after oven-
drying, and the volume change is reduced to a linear measurement by taking the
cube root:
p
3
COLE ¼ ð V m =V d Þ 1 ð12:9Þ
Where V m is the volume moist and V d is the volume dry. Volumes are obtained
from the reduction in weight when submerged in water, which equals the weight of
the water displaced. For example, if the reduction in weight is 100 g (weight), the
3
volume is 100 cm . A COLE of 53 percent is considered low, 3 to 6 percent
moderate, and 46 percent high for residential construction (Hallberg, 1977).

12.14.4 Slaking

Shale may be subjected to a slaking test that involves measuring the weight loss
after wetting and tumbling in a rotating drum (ASTM D-4644). Dry clods of soil
also may slake when immersed in water as the adsorptive power may be so great

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