Permanent Deformation Behavior of Granular Materials and the Shakedown Concept

TLDR

The shakedown concept, used to describe cyclic loading behavior in engineering structures, suggests a critical stress level—called the shakedown limit—between stable and unstable pavement conditions, which was investigated through repeated load triaxial tests on crushed rock aggregates. The study aimed to define a modified set of shakedown responses for granular materials. The authors performed repeated load triaxial tests on crushed rock aggregates at various stress levels to establish the shakedown limit and develop the modified response set. The tests revealed that permanent deformation accumulated with loading, partially matched existing shakedown predictions, and the new description offers a powerful assessment tool and design chart for unbound pavement bases.

Abstract

The shakedown concept has been used to describe the behavior of conventional engineering structures under repeated cyclic loading. The possibility has been raised that a critical stress level exists between stable and unstable conditions in pavement. According to the “shakedown” concept, this level is termed the “shakedown limit.” Several repeated load triaxial tests were performed on crushed rock aggregates at different stress levels. The resulting permanent deformation, which accumulated with the repeated loading, was described and compared with the types of responses usually described by the shakedown approach. The existing shakedown approach can describe some, but not all, of the observed responses. Thus, a modified set of possible responses was defined in shakedown terms. The method of description could provide a powerful material assessment and pavement design tool for engineering unbound pavement bases. A design chart derived from the data illustrates a possible design approach.