➤ Flexible
pavements: These are the pavements which have very less flexural strength. They
transfer the load coming over them directly to the lower layers through grain
to grain contact. So the load transfer largely depends upon the type of the
grains/aggregates that are used in the construction of the pavement. If the aggregates are well compact/ well
graded then their grain to grain contact will be good and they can transfer the
load to a wider area. The flexible pavement has the following layers:
(a) Wearing
course
(b) Sub base
course
(c) Base
course
(d) Sub
grade
The stress
intensity is maximum at the top layer of the pavement and it decreases with
depth. Due to ability of the pavement to transfer the loads to lower layers in
the truncated form, the layer concept has been introduced for its construction.
The pavements is made of layers of different materials. The top layer is made
of superior material, because it has to face the largest stresses, and the
lower layers are constructed with with inferior materials. So the wearing course is made of the superior
quality material and sub-grade can be constructed of the locally available
earth too. The materials like bituminous concrete, is best to use as the
surface course and the others like water bound macadam, and other crushed
aggregates, gravels can be used for the base and sub base courses. The flexible
pavements are designed with the help of the empirical design charts or some
equations taking into account the various design factors. Some semi-empirical
and theory methods are also available for the design of the flexible pavements.
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