Page 108 - Geotechnical Engineering Soil and Foundation Principles and Practice

The Soil Profile
The Soil Profile 103

Figure 5.2
Typical damages
from an expansive
clay B horizon.
This crack pattern
indicates
shrinkage.

Figure 5.3
Basement wall and
sewer pipe being
pushed in by
wet-dry cycling of
an expansive clay
B horizon. This
may happen years
after
construction, as
cycling is required
to compress loose
soil backfill placed
against the outside
of the wall. Also a
severe problem
with expansive
shale C horizons
as in the Denver
area.

Moisture cycling of a B horizon containing expansive clay creates a ‘‘subangular
blocky’’ structure with the individual blocks or peds measuring a centimeter or so
across. Clay coatings on the outside of the individual peds are planes of weakness
that maintain the blocky structure. A blocky structure therefore is diagnostic of
expansive clay.

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