Page 120 - Geotechnical Engineering Soil and Foundation Principles and Practice

The Soil Profile
The Soil Profile 115

5.6.4 Soil Classification
Soil classification follows a biological model, from top down consisting of order,
suborder, great soil group, family, and series.

Classical names for great soil groups like Podzol, Brunizem, and Chernozem are
Russian in origin, and respectively mean ashy, brown earth, and black earth, in
reference to the color of the topsoil. These soil groups are called ‘‘zonal soils’’
because they bear close relationships to climatic zones.

More relevant in engineering is a system developed multinationally by soil
scientists, called soil taxonomy. This system is based on measured soil properties,
and new words were coined to try and convey the most significant properties.
The names therefore are useful if one can penetrate their complicated system
and polyglot origins.

The ten soil orders are described in the following paragraphs, arranged more or
less according to increasing degree of weathering. A hypothetical relationship of
soil orders to climate is shown in Fig. 5.8.

5.6.5 Ordering the Orders
Names for soil orders normally are not a major concern in engineering, but can
be helpful for characterizing a particular soil series. For example, if a soil series
is identified as a ‘‘Histosol’’ or ‘‘Vertrisol’’ it should raise some alarm bells for the
engineer. Other soil orders are much less threatening, but the names nevertheless
can reveal important properties.

Histosol means ‘‘tissue soil’’ and signifies bog soils, peat, and organic muck. In
a soil classified as ‘‘Cryofibrist,’’ ‘‘cryo’’ means cold, ‘‘fibr’’ implies fibrous, and
‘‘ist’’ is the designation for Histosol. The order is designated by the last three or
four letters in a soil name, so when ‘‘ı´st’’ is appended to the end of a soil name one

Figure 5.8
Generalized
relationship
between soil
orders of the
Seventh
Approximation
and climate.

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