Introduction of Soil ( As a Construction Material )

Soil is very essential highway material and construction materials because of the under following reasons : 

 soil subgrade is part of the pavement structure and the design and behaviour of pavements, the flexible pavements depend to a great extent on the subgrade of  soil. soil is also one of the principal materials of construction in soil embankments and in stabilized soil base and subbase courses of structure.

In view of the wide diversity in different soil type, it is desirable to classify them into groups of soils possessing similar physical properties of soil. Many methods have been in use for this soil classified purpose.

Soils are normally classified on the basis of simple laboratory tests such as grain size analysis and consistency tests. Soil compaction is very important in highway construction as compacted subgrade improves the load supporting ability of pavement, in turn resulting in decreased pavement thickness requirement. Compaction of earth embankments would result in decreased settlement. Thus the behaviour of soil subgrade material could be considerably improved by adequate compaction under controlled conditions. The lab. compaction test results of soils are useful in specifying the moisture content at which a soil should be compacted and the dry density that should be aimed at the construction site.

There are a number of test methods for measuring soil shear strength; some of them give the strength parameters of the soil, other methods are empirical and give only arbitrary strength values of soil.

The types of the strength tests may be classified as shear tests, bearing tests and penetration tests.The california Bearing Ratio ( CBR )  test is essentially a penetration test which is carried out either in the laboratory or in the field site. This test is suitable for the evaluation of strength of soil and aggregates.The method has an important place among highway material testing programme, as it has been extensively correlated with flexible pavement design and performance.

There are several soils which are unfit for highway material, since they can not be used as such in the base course, sub-base or the subgrade. The strength and durability properties of these soils can be improved to the desired extent by adopting a stabilization. One of the widely used methods of stabilization is soil-cement which is applicable to a fairly wide range of soil types.