|
Sub grade soil is an integral part of the road pavement structure as it
provides the support to the pavement from beneath.
The sub grade soil and its properties are important in the design of pavement
structure.
The main function of the sub grade is to give adequate support to the pavement
and for this the sub grade should possess sufficient stability under adverse
climatic and loading conditions.
Therefore, it is very essential to evaluate the sub grade by conducting tests.
The tests used to evaluate the strength properties of soils may be broadly
divided into three groups:
- Shear tests
- Bearing tests
- Penetration tests
Shear tests are usually carried out on relatively small soil samples in the
laboratory.
In order to find out the strength properties of soil, a number of
representative samples from different locations are tested.
Some of the commonly known shear tests are direct shear test, triaxial
compression test, and unconfined compression test.
Bearing tests are loading tests carried out on sub grade soils in-situ
with a load bearing area.
The results of the bearing tests are influenced by variations in the soil
properties within the stressed soil mass underneath and hence the overall
stability of the part of the soil mass stressed could be studied.
Penetration tests may be considered as small scale bearing tests in which the
size of the loaded area is relatively much smaller and ratio of the penetration
to the size of the loaded area is much greater than the ratios in bearing
tests.
The penetration tests are carried out in the field or in the laboratory.
|
