Investigating the Mechanical Behaviour of Unbound Granular Material (UGM) for Road Pavement Construction Applications: A Western Victoria Case Study

Abstract

The behaviour of unbound granular materials (UGMs) used in road construction is crucial in determining the longevity and performance of road pavement. Geotechnical analysis can assist engineers in selecting suitable materials and designing road pavements that meet industry standards. This paper presents the results of laboratory geotechnical tests conducted on unbound granular materials (UGMs) collected from three sites (Roses Gap, Rules East, and Polkemmet Road) in Horsham, Victoria, Australia. UGMs were investigated for their mechanical behaviour and suitability as subgrade materials for road pavements. The study utilised laboratory geotechnical tests, including particle size distribution (PSD), Atterberg limits, compaction (Proctor) test, unconfined compressive strength (UCS), California Bearing Ratio (CBR), and repeated load triaxial (RLT) tests, to evaluate the physical and mechanical properties of the UGM samples. The study indicates that UGM samples collected from different locations displayed variations in their geotechnical properties, such as particle size distribution, water absorption, and CBR strength. Roses Gap samples showed weak cohesion properties, and significant vertical displacements after repeated triaxial tests. However, among the samples in this site, samples with higher clay content (RG21) demonstrated the most promise in triaxial tests. Similarly, the Rules East samples were found to be suitable for low-traffic subgrades due to their satisfactory CBR and RLT testing results, albeit with little cohesion from clay content. Out of three locations, Polkemmet samples were identified as potential subgrade applications, with PR12 being the top recommendation overall. It satisfied PSD, CBR, and RLT test conditions due to acceptable particle size in the largest range, highest CBR strength value, and lowest permanent displacement. The study's findings provide useful information for the design of road pavements using these materials and the characterisation of rural materials around the Horsham region for future use in various other contexts.