Strain measurements in flexible pavements under heavy vehicle axle loads

Highway traffic in New Zealand is carried by flexible granular pavements smfaced with sprayed seals or thin layers of bituminous mixes. The primaI}' design criteria for such pavements is to limit the vertical compressive strain in the subgrade, because excessive accumulations of the strain ultimately result in surface rutting and distress. The research described in this paper involves roads in service and New Zealand's facility for accelerated testing of the interaction between full-scale pavements and vehicles. Three recent projects at the test facility and an instruini:nted insitiiroad are descnDed. The primary finding in both the field and test track projects was that the actual strains in the sub grade were up to over three times that predicted by the pavement performance model, but the pavements still performed satisfactorily.