Important factor in the pavement design
Traffic is the most important factor in the
pavement design. The key factors include contact pressure, wheel load, axle
configuration, moving loads, load, and load repetitions.
Contact pressure: The tyre pressure is an important factor, as
it determine the contact area and the contact pressure between the wheel and
the pavement surface. Even though the shape of the contact area is elliptical,
for sake of simplicity in analysis, a circular area is often considered.
Wheel load: The next important factor is the wheel load which
determines the depth of the pavement required to ensure that the subgrade soil
is not failed. Wheel configuration affect the stress distribution and
deflection within a pavemnet. Many commercial vehicles have dual rear wheels
which ensure that the contact pressure is within the limits. The normal
practice is to convert dual wheel into an equivalent single wheel load so that
the analysis is made simpler.
Axle configuration: The load carrying capacity of the
commercial vehicle is further enhanced by the intro-duction of multiple axles.
Moving loads: The damage to the pavement is much higher if the
vehicle is moving at creep speed. Many studies show that when the speed is
increased from 2 km/hr to 24 km/hr, the stresses and deflection reduced by 40
per cent.
Repetition of Loads: The influence of traffic on pavement not
only depend on the magnitude of the wheel load, but also on the frequency of
the load applications. Each load application causes some deformation and the
total deformation is the summation of all these. Although the pavement
deformation due to single axle load is very small, the cumulative effect of
number of load repetition is significant. Therefore, modern design is based on
total number of standard axle load (usually 80 kN single axle).
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