Modelling permanent deformation behaviour of unbound granular materials

A state of the art is presented on modelling permanent deformation behaviour of unbound granular materials. The existing numerical models are verified by a series of laboratory repeated load tests. A new model is introduced expressing the accumulated permanent axial strain at any given number of cycles as a function of applied stresses, taking into account the maximum shear stress ratio and the length of the stress path in pq space. The results show similarities with the concept of the shakedown theory. At low levels of stress ratios the accumulation of permanent strain ceases, resulting in an equilibrium state. However, there are indications of the existence of a threshold stress ratio, known as the shakedown limit, beyond which the material experiences incremental collapse or gradual failure. (C) 1998 Elsevier Science Ltd. All rights reserved.