Unbound Granular Pavements; Design With Understanding : A Revision And Extension

The original paper, Rallings (2018), presented a rudimentary behavioural model of the response of unbound granular pavements (UGPs), ones that are founded on compacted clay subgrades, to passages of single wheel loads. The following amends and expands the original model and includes new terms and concepts. The proposed model is based on the assumption that elevated subgrade shear strains in conjunction with a strain-controlled mechanism disturb the fabric of the overlying granular materials (OGM) causing reductions in their stiffness and in the UGP’s load carrying capacity, essentially its ability to maintain its surface shape. It is proposed that short term falls in the subgrade shear strength and/or increases in the frequency of the heaviest loads within the wheel load spectrum are the common major contributors to the degradation of a UGP’s load carrying capacity. The proposed model provides a direct and simple means to predict the response of a UGP to load passages, allowing designers and asset managers alike to distinguish between those wheel loads that pose a potential threat to the UGP from those that do not.