Characterization of permanent axial strain of granular materials subjected to cyclic loading based on shakedown theory

The Werkmeister’s criteria are widely utilized for characterizing the permanent axial strain behaviour of granular materials. These criteria are based on shakedown theory and are adopted in the European Standards. In this paper, the limitations of Werkmeister’s criteria and the simplification adopted in European Standard are discussed. To overcome these shortcomings, new criteria on characterizing the shakedown ranges of granular materials are proposed. The mathematical expression and physical meanings of the proposed criteria are presented and discussed in detail. It is noteworthy mentioning that, based on the new criteria, the characterizing of shakedown range only assesses the whole development trend of permanent axial strain occurred during the secondary cyclic compression period. Firstly, the performances of the new criteria and Werkmeister’s criteria are compared using the test data from existing literature. It can be concluded that the new criteria are capable of giving quite satisfactory prediction. Furthermore, in this study, several cyclic triaxial tests with step-wisely increasing cyclic deviatoric stress were conducted to verify the new criteria. The test results show a transitional range, which indicates the onset of the disruption of external loading to the original stable structure of granular materials.