Design of road foundations
Research has been conducted into the fundamental mechanical properties of a granular material. This has involved the use of both a repeated load triaxial apparatus and a new hollow cylinder apparatus, which has required development and modification. Building on the foundation of earlier research at Nottingham, models have been developed which predict the stress-strain behaviour of a dry granular material under any combination of applied stresses. This includes repeatable elastic behaviour and the development of irrecoverable plastic strain. The accuracy of these models has been tested as far as possible using available test equipment. The effects of varying particle gradation, degree of compaction, maximum particle size and mineral type have been explored using a repeated load triaxial apparatus. The effect of moisture has also been investigated with respect to both full and partial saturation. A computer program (GRANMAT) has been written, which makes use of the stress-strain equations developed, to analyse a road pavement structure consisting of thin bituminous surfacing, granular base and subgrade. The reliability of the program has been assessed and areas of necessary improvement indicated. In-situ testing at a number of road sites is described and analysed with respect to both the effect of compaction on a granular road foundation and the use of a number of in-situ test devices. Finally, the information gained, in the laboratory and on site, is brought together in a series of design suggestions for granular road foundations, with particular reference to results from the GRANMAT computer program.