Page 259 - Geotechnical Engineering Soil and Foundation Principles and Practice

Soil Consistency and Engineering Classification
254 Geotechnical Engineering

Figure 12.5
Linear relations
between PI and
percent clay.
Ratios were
defined by
Skempton (1953)
as activity indices,
which are shown
in parentheses.
The Shellhaven
soil clay probably
is smectite.

þ
Table 12.1 Na smectite (montmorillonite) 3–7
Activity indices of Ca 2þ smectite (montmorillonite) 1.2–1.3
selected clay Illite 0.3–0.6
minerals (after Grim, Kaolinite, poorly crystallized 0.3–0.4
1968) Kaolinite, well crystallized 50.1

is applied to the data in Fig. 12.6 with k ¼ 10, then A ¼ 1.23 0.04 where
the value is the standard error for a number of determinations n ¼ 81.
This identifies the clay mineral as calcium smectite, which is confirmed by X-ray
diffraction.

12.7 LIQUID LIMIT AND COLLAPSIBILITY

12.7.1 Concept

A simple but effective idea was proposed in 1953 by a Russian geotechnical
engineer, A. Y. Denisov, and later introduced into the U.S. by Gibbs and Bara of

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