DHARM94 GEOTECHNICAL ENGINEERING
The identification procedures given above may have bearing on preliminary classifica-
tion of the soil, dealt with in later sections.
4.3 SOIL CLASSIFICATION—THE NEED
Natural soil deposits are never homogeneous in character; wide variations in properties and
behaviour are commonly observed. Deposits that exhibit similar average properties, in gen-
eral, may be grouped together, as a class. Classification of soils is necessary since through it an
approximate, but fairly accurate, idea of the average properties of a soil group or a soil type is
obtainable, which is of great convenience in any routine type of soil engineering project. From
engineering point of view, classification may be made based on the suitability of a soil for use
as a foundation material or as a construction material.
There is, however, some difference of opinion among soil engineers as to the importance
of soil classification and the broad generalisation of the properties of various groups. This is
largely because of different points of view and emanates primarily from the difficulty in form-
ing soil groups in view of very wide variations in engineering properties which are too large in
number. Thus, it is inevitable that in any classification there will be border cases which may
fall into two or more groups. Similarly, the same soil may be placed into groups that appear
radically different under different systems of classification.
In view of this, classification is to be taken merely as a preliminary guide to the engi-
neering behaviour of the soil, which cannot be fully or solely predicted from the classification
alone; certain important soil engineering tests should necessarily be conducted in connection
with the use of soil in any important project, since different properties govern the soil behav-
iour in different situations. The understanding of the engineering behaviour of a soil should be
the more important issue.
4.4 ENGINEERING SOIL CLASSIFICATION—DESIRABLE FEATURES
The general requirements of an ideal and effective system of soil classification are as follows :
(a) The system should have scientific approach.
(b) It should be simple and subjective element in rating the soil should be eliminated as
far as possible.
(c) A limited number of different groupings should be used, which should be on the basis
of only a few similar properties,
(d) The properties considered should have meaning for the engineering profession.
(e) It should have fair accuracy in indicating the probable performance of a soil under
certain field conditions.
(f) It should be based on a generally accepted uniform soil terminology so that the clas-
sification is done in commonly well-undestood and well-conversant terms.
(g) It should be such as to permit classification of a soil by simple visual and manual
tests, or at least only by a few simple tests.
(h) The soil group boundaries should be drawn as closely as possible where significant
changes in soil properties are known to occur.