Geology Reference
In-Depth Information
11
CHAPTER ELEVEN
CHAPTER ELEVEN
Classification of
Soils for Engineering
Purposes
Classification of
Soils for Engineering
Purposes
(Referenced Documents: AASHTO M 145
and ASTM D 2487)
To describe, in general, a specific soil without listing values of its param-
eters, it is convenient to have some kind of generalized classification
system. In practice, a number of classification systems have been devel-
oped by different groups to meet their specific needs. Some examples are
the AASHTO classification system, Unified Soil Classification System,
and Federal Aviation Administration (FAA) classification system. All
classifications of soil for engineering purposes use Atterberg limits (at
least the liquid and plastic limits) and grain-size analysis as delimiting
parameters.
The first two systems cited are covered in this chapter. In each case,
one or more sample classifications are given to assist in understanding
the system. Inasmuch as these classifications are based on Atterberg
limits and grain-size analysis, laboratory procedures for which have
been presented in Chapters 7 through 10, Chapter 11 presents no new
laboratory procedure. Instead, the emphasis is on classification of soils
once Atterberg limits and grain-size analyses are known.
INTRODUCTION
AASHTO stands for the American Association of State Highway and
Transportation Officials; therefore, this classification system is widely
used in highway work. Required parameters for each classification by
this system are grain-size analysis, liquid limit, and plasticity index.
AASHTO
CLASSIFICATION
SYSTEM
145
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