Page 419 - Corrosion Engineering Principles and Practice

388 C h a p t e r 1 0 C o r r o s i o n i n S o i l s a n d M i c r o b i o l o g i c a l l y I n f l u e n c e d C o r r o s i o n 389

identification scheme defines eleven soil types on the basis of their
respective proportions of clay, silt, and sand, that is, sand, loamy
sand, sandy loam, sandy clay loam, clay loam, loam, silty loam, silt,
silty clay loam, silt clay, and clay.
A newer soil classification system has evolved in the United
States to classify soils globally, at any location. In this universal
classification system, soils are considered as individual three-
dimensional entities that may be grouped according to their
physical, chemical, and mineralogical properties. The system uses a
hierarchical approach, with the amount of information about a soil
increasing down the classification ladder. From top to bottom, the
hierarchy is structured in the following categories: order, suborder,
great groups, subgroups, families, and series. Further details are
provided in Table 10.2.

Basis for
Category Classification Example(s) Comments
Order Differences in Entisol, Vertisol, Nine orders for
measurable Inceptisol, mineral soils and
and visible Aridisol, Mollisol, one order for all
characteristics Spodosol, organic soils.
of soil horizons. Alfisol, Ultisol,
Oxisol, Histosol
Suborder Differences in Aquod, Udult Grouping according
development to accumulation of
characteristics. soluble materials,
presence or
absence of
B horizons,
mineralogy, and
chemistry.
Great Presence or Kandihumult Relative thickness
group absence of of horizons is
certain horizons important.
Subgroup Typical or Typic Coded as either
dominant Kandihumult the great group
concept of the name with the
great group. “typic” prefix, or a
combination of great
group names.

TABLE 10.2 Soil Classification System Using Hierarchical Approach