Impact of introducing longer and heavier vehicles on the bearing capacity of pavement subgrades

Abstract

Increasing the maximum permissible gross weight of vehicles from 64 tons to 74 tons on Swedish highways may significantly increase deformation in subgrades requiring extensive and expensive measures for maintenance deep down in the structures. Even though the individual axle load remains the same, longer and heavier vehicles will contain higher proportions of tandem and tridem axles and the total load will be superposed on to the subgrade resulting in higher deformations. In this study, the relative impact of single, tandem and tridem axles on subgrade deformation was analyzed based on calculations in a pavement design software called ERAPave. Three structures with different layer thicknesses and varying material properties during the spring-thaw and summer period were analyzed. In general, it was observed that the relative impact is dependent on the thicknesses and material properties of the pavement structure and the subgrade. Weaker subgrade is more affected by the tridem axle followed by tandem and single axle. The tridem axle is more damaging to the sub-grade for thicker and stiffer structures. In certain cases, the single axle showed more impact on the top of the subgrade. The tridem axle showed more vertical deflection in all cases that may induce increased fatigue cracking of the asphalt concrete (AC) layer. Duration of loading was higher for the tridem axle which has more damage potential. Thus, for the whole vehicle, containing more tridem axles, the effects may be superposed resulting in greater damage. On the other hand, the higher load carrying capacity of the tandem and tridem axle configurations will reduce the number of trips required to carry the same amount of goods. This may compensate for the increased damage to the subgrade and the impact on the life cycle of the pavement.