Variation Of The Observed Surface Strains Caused By Uniform And Non-Uniform Contact Pressures Using A Finite Element Method

The current practice in pavement design is to use a circular uniformly distributed load as the input to ascertain the maximum strains in the pavement. This is not the reality; tyre-pavement contact pressure distributions are very complex. The distress on the surface of the pavement in the form of rutting and surface initiated cracking is very much dependent on these complex pressure distributions. This study investigates the effects that non-uniform contact pressure distributions have in comparison to the traditional circular loading on the initiation and rate of accumulation of this distress. The problem has been modelled using the CAPA-3D finite element software. The traditional circular load was modelled. The strains in a number of key locations were recorded and measured. Then the non-uniform loading was modelled using the same procedure. What was of particular interest was the difference in the peak surface strains and positions between the two different methods of loading. The non-uniform loading created significantly larger strains under the contact patch. The non-uniform loading also created significant shearing forces close to the surface and under the contact area. This leads to a greater propensity for the surface to develop rutting and also for cracking. The differences started to become less evident with distance from the loading area for the principal stresses. It is recommended that for the design of surface layers non-uniform contact pressures should be used.