The Routine Laboratory Assessment of the Performance of Coarse Granular Materials for Pavement Foundation Design

Abstract

A performance based specification for road foundations potentially allows any material that can be assessed as ‘fit for purpose’ to be used, and encourages the wider use of marginal and recycled/secondary materials. For such a specification to be implemented information of material stiffness and resistance to permanent deformation is required for analytical design, and tests must be available to validate the design parameters onsite. Therefore a routine, economical laboratory-scale test needs to be developed to assess the performance and suitability of any poten tial foundation material to provide data for design, and ideally such a test should link to the field-based compliance testing. To facilitate this a large-scale laboratory test has been developed to assess the performance of coarse granular materials, typical of those used in UK pavement foundations. The test utilises a heavy duty steel box with a synthetic base layer, and portable test devices. This paper evaluates the performance of the test by comparing the results from a compacted sample of a typical site won “capping” material to associated field data. To validate the test methodology analysis of the stiffness test data for each layer compacted within the tests sample is presented. The effects of a soft and rigid base condition, and wetting and drying of the material is shown to have a significant effect on the measured values of both stiffness and strength. However, there appears a reasonable relationship between the laboratory results for the soft base condition and the field data.