The assessment of coarse granular materials for performance based pavement foundation design

The need to use more recycled and marginal materials in pavement foundations is encouraging moves towards performance based specifications. Such an approach needs data on the fundamental material parameters of stiffness and resistance to permanent deformation (strength) to allow analytical design and achieve comparable compliance testing on site. Whilst a number of laboratory and field tests to measure such performance exist, all have limitations relative to either the particle size of materials that can be tested and/or correlation between the laboratory and field derived data. This paper presents the development of a large scale resiliently lined steel laboratory material box tests proposed for routine material assessment. The test utilises a Lightweight Deflectometer, similar to that proposed for field compliance testing to provide performance data from compacted large particle size granular materials. The system developed utilises a “soft” base condition to replicate typical subgrade stiffness and allows wetting and drying of materials to assess their environmental stability. The results show that such a test can simply provide suitable data for performance based design, but consideration needs to be given to the water content of materials, the time of testing after compaction, and the use of appropriate boundary conditions. These findings have both implications not only for the developed tests but for field compliance testing of pavement foundations.