INFLUENCE OF AXLE GROUP SPACING ON PAVEMENT DAMAGE

Current pavement design guides do not consider the effects of axle spacings. However, in many jurisdictions, higher loads on dual and triple axles are allowed for higher axle spacings. This practice is examined from a pavement viewpoint to ensure that dual or triple axles do not cause disproportionately greater damage than single axles. Damage effects of dual and triple axles on flexible pavements were evaluated as a function of axle spacing. The evaluation was based both on measured and calculated pavement responses to axle loads. Load equivalency factors are significantly influenced by pavement response parameters and by summation methods used for their derivation. The results display significant influence of the axle spacing on pavement damage. This indication should be taken into account when determining legal load limits on the axles. The AASHTO Guide appears to underestimate the damaging effect of dual and triple axles in comparison with single axles.