Estimation of resilient modulus of unbound granular materials using Clegg impact value and field stress levels

Resilient modulus (Mr) is an important property that controls the performance of pavement materials under dynamic wheel loads. Mr can be determined in the laboratory from repeated load triaxial tests and is defined as the ratio of the deviator stress to the recoverable strain after a number of load applications. Inherently, it is a challenge to perform repeated load triaxial tests as routine tests due to their rather complicated, time-consuming and expensive procedure. Hence, researchers have attempted to develop empirical estimation models based on the mechanical properties of pavement materials, such as the California bearing ratio and the unconfined compressive strength or physical properties of materials. This study examines the correlation between the Clegg impact value (CIV) and the Mr of unbound granular materials (UGM) of pavements. The Clegg impact hammer test provides a parameter based on the response of the material to dynamic, rather than static or gradual, loading. Fourteen different unbound granular materials with particle sizes ranging from 7 mm to 19 mm used in the study. The results indicate that there exist a good to strong correlation between the resilient modulus Mr and Clegg impact hammer value, CIV, with the highest R2 value of 0.82 and the average R2 value of 0.76, from 48 stress levels used in Mr tests.