Permanent deformation behaviour and model of crushed rock base

Abstract

This study aims to report on the permanent deformation behaviour of a crushed rock base (CRB) subjected to repeated cyclic loads from repeated load triaxial tests with different stress levels in order to gain more understanding of such materials for Western Australian roads based on mechanistic-empirical pavement design and analysis. As is well known, road surface rutting is generally considered one of the main types of damage in flexible pavements. One factor contributing to the rutting of an asphalt road surface is the excessive deformation of a base course layer. CRB is the commonly used base course material in the Western Australia metropolitan area. In recent times, CRB has not been fully characterised based on fundamental pavement analysis, therefore the behaviour of a plastic deformation response of CRB under service loads is not well understood. In this study, CRB was mechanically investigated and the shakedown concept was utilised to explain its behaviour under cyclic loading conditions, and the limited use of CRB subjected to various degrees of stress conditions was defined. While the plastic shakedown limit of an unbound granular material is known from macro-mechanical observations of its response following the shakedown concept, the limitations of the accumulated plastic deformation in an unbound granular layer causing deterioration in pavements is predictable. The investigation was designed such that compacted CRB samples, at a compaction condition of 100% maximum dry density and 100% optimum moisture content, were subjected to applied load conditions at various stress levels (the ratio of a vertical principal stress, σ1 and a horizontal principal stress, σ3). The limitations on the use of CRB as a base course material will be introduced, as well as its appropriate working stress ranges.