Page 251 - Geotechnical Engineering Soil and Foundation Principles and Practice

Source: GEOTECHNICAL ENGINEERING
12 Soil Consistency

and Engineering

Classification

12.1 CLASSIFICATION AND SOIL BEHAVIOR

12.1.1 Classification and Engineering Properties
Soil properties that are of most concern in engineering are strength and volume
change under existing and future anticipated loading conditions. Various tests
have been devised to determine these behaviors, but the tests can be costly and
time-consuming, and often a soil can be accepted or rejected for a particular use
on the basis of its classification alone.

For example, an earth dam constructed entirely of sand would not only leak, it
would wash away. Classification can reveal if a soil may merit further
investigation for founding a highway or building foundation, or if it should be
rejected and either replaced, modified, or a different site selected. Important clues
can come from the geological and pedological origin, discussed in preceding
chapters. Another clue is the engineering classification, which can be useful even if
the origin is obscure or mixed, as in the case of random fill soil.

12.1.2 Classification Tests
Engineering classifications differ from scientific classifications because they focus
on physical properties and potential uses. Two tests devised in the early 1900s by a
Swedish soil scientist, Albert Atterberg, are at the heart of engineering
classifications. The tests are the liquid limit or LL, which is the moisture
content at which a soil become liquid, and the plastic limit or PL, which is
the moisture content at which the soil ceases to become plastic and crumbles in
the hand.

Both limits are strongly influenced by the clay content and clay mineralogy,
and generally as the liquid limit increases, the plastic limit tends to decrease.

246 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2007 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.