Understanding Unbound Granular Pavements (UGPs)

Mr Ralph Rallings

UGPs provide the backbone of the Australia’s rural pavements network.  Their adequate performance is vital to transport efficiency. The presentation will describe a proposed behavioural model for UGPs; one that is consistent with the behaviour of compacted clays and dense granular pavement materials under load. The model is directed towards the prediction of the nature of the response of UGPs to load passages. Elastic, elastoplastic and plastic responses are possible. The degradation of the load carrying capacity of UGPs, essentially their ability to maintain shape under load passages is attributed primarily to stiffness reductions of the unbound granular pavement materials.  These reductions occur whenever subgrade shear strains are large enough to cause non-recoverable increases in the void content of the overlying granular pavement materials. The model predicts that quite short-term increases in subgrade shear strains, caused either by a fall in subgrade strength or by an increase in the frequency of the heaviest loads within the wheel load spectrum may result in a rapid and permanent loss of load carrying capacity.  The presentation will outline an estimation procedure for subgrade cover.  The procedure is based on the perceived consequences of a loss of load carrying capacity.

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