Page 310 - Geotechnical Engineering Soil and Foundation Principles and Practice

Compaction
Compaction 305

Table 13.2
Applications of
compaction
equipment.

Adapted from Caterpillar Performance Handbook, ß Caterpillar Inc

also reduces the strength of the compacted soil and can increase dispersion of
clays. In other words, a small amount of chemical can make a soil easier to
compact by making it weaker. In recognition of this, chemical ‘‘compaction aids’’
are not permitted in most compaction specifications.

Whereas hydrated lime flocculates an active clay soil, increasing the OMC and
lowering the compacted density, chemical compaction aids do just the opposite.
Field inspectors should be wary of water additions that have a soapy feel or tend
to foam. Many aids are rendered ineffective by expansive clay minerals that
remove organic chemicals by adsorption between clay layers.

CaCl 2 , calcium chloride, also is the reverse of a compaction aid as it increases the
surface tension of water, and densification occurs as a result of higher suction
forces when the soil dries out. Calcium chloride occasionally is used to increase
the surface density of granular unpaved roads and as a dust palliative, but has a
low pH that accelerates rusting.

Another chemical additive, lignin, which is a byproduct from paper manufactur-
ing, is used as a dust palliative and behaves as a glue until rain leaches it out.

13.14 STATISTICS OF COMPACTION

13.14.1 Variability and Accuracy of Testing

The more variable a material, the more tests are required to characterize the final
product, and soil can be quite variable. The most common statistical parameter is

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