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Flexible pavements will transmit wheel load stresses to the lower layers by
grain-to-grain transfer through the points of contact in the granular structure
(see Figure 1).
Figure 1:
Load transfer in granular structure
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Deflection on flexible pavement
The wheel load acting on the pavement will be distributed to a wider area, and
the stress decreases with the depth.
Taking advantage of this stress distribution characteristic, flexible pavements
normally has many layers.
Hence, the design of flexible pavement uses the concept of layered system.
Based on this, flexible pavement may be constructed in a number of layers and
the top layer has to be of best quality to sustain maximum compressive stress,
in addition to wear and tear.
The lower layers will experience lesser magnitude of stress and low quality
material can be used.
Flexible pavements are constructed using bituminous materials. These can be
either in the form of surface treatments (such as bituminous surface treatments
generally found on low volume roads) or, asphalt concrete surface courses
(generally used on high volume roads such as national highways).
Flexible pavement layers reflect the deformation of the lower layers on to the
surface layer (e.g., if there is any undulation in sub-grade then it will be
transferred to the surface layer).
In the case of flexible pavement, the design is based on overall performance of
flexible pavement, and the stresses produced should be kept well below the
allowable stresses of each pavement layer.
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