Abstract:
This paper investigates flexible pavements designed using CBR methods subjected to fatigue
and rutting strain analysis. The experiment was investigated with the layered elastic analysis
software EVERSTRESS. The three known CBR methods namely the Asphalt Institute, the
National Crushed Stone Association and the Ghanaian CBR methods were experimented to
evaluate their fatigue strain and rutting deformation characteristics. The elastic properties
of the materials were determined. Structural thickness requirement of the pavements were
experimented using their respective design charts for a traffic volume of 3000 vehicles/day
and expected load repetition of 3.2 x 106 cycles . Stresses, strains and deflections due to 80
kN single axle load having a tyre pressure of 690.78 kPa were computed by analyzing the
effect due to 20 kN single axle load spaced 30.5 mm centre to centre. Strain evaluation was
carried out both for the underside of the asphalt bound layer and at the top of the sub-grade
which is 15.25 mm midway between the 20 kN axle loads. Pavement responses were also
analyzed using both the Heukelom and Klomp Model and the Asphalt Institute Model.
Results showed that the vertical compressive strains at the top of the sub-grade were found
to be -923.033, -902.7 and -771.24μ for Asphalt Institute CBR, NCSA CBR and the
Ghanaian CBR methods respectively. The horizontal tensile strains on the underside of the
asphalt bound layer were 355.50, 355.34 and 371.91μ for Asphalt Institute CBR, NCSA
CBR and the Ghanaian CBR methods respectively. It was also found out that the computed
vertical compressive strains for the Heukelom and Klomp Model were more than the
permissible values. The fatigue damage factors were found to be less than 1.0 while therutting damage factors were greater than 1.0 for both models. It was further established
that flexible pavements designed are prone to failure due to rutting deformation..
