Abstract:
Unbound granular material is used in the pavement structure and usually comprises the bulk of the
structural and foundation layers of a typical South African pavement. The term ‘unbound granular
material’ refers to the classification of natural material, which has not been modified in any way.
Various mechanistic-empirical models for the resilient response of unbound granular material have
been developed over the years. However, few have incorporated important influencing parameters such
as moisture or density on the basic stress-strain relationship or linked variables of the models to basic
engineering properties of unbound granular material.
This study builds on previous work by Theyse (2008a) and the cord modulus model developed by
Theyse (2012). The Theyse (2012) model was selected to be further investigated, since it modelled the
trends observed in the data realistically. The model depicts the stress dependent behaviour of unbound
granular material, where an increase initial modulus is observed for increasing confinement pressure,
as well as initial stress-softening with increasing stress ratio followed by stress stiffening.
The model was calibrated for all bulk material samples under consideration in this thesis. The calibration
process included linking variables of the model to mathematical functions that approximate the trends
observed when variables were considered against level of saturation. A parametric analysis indicated
that the saturation and stress-dependent cord modulus model realistically predict material behaviour.
The saturation and stress-dependent cord modulus model was refined further and calibrated for crushed
and natural unbound granular material. This refinement did not negatively influence the accuracy or
ability to realistically predict the material behaviour.
Basic material properties could be linked to predictive statistical distributions that could estimate the
range of modulus values that can be expected for the material under consideration. However, the
variables of the saturation and stress-dependent cord modulus model could not be linked to basic
material properties due to the limit set of results
available.
