Packing theory-based Framework for Performance Evaluation of Unbound Granular Materials

Abstract: Enhancing the load bearing quality of granular layers is fundamental to optimize the structural performance of the pavements. Unbound granular materials are one of the most used materials in the base layers of pavements. There have been growing interests on the behavior of unbound granular material in road base layers. Both design of a new pavement and prediction of service life need proper characterization of unbound granular materials, which is one of the requirements for a new mechanistic pavement design methods.Adequate knowledge of the strength and deformation characteristics of unbound layers in pavements is essential for proper thickness design, residual life determination, and economic optimization of the pavement structure. The current knowledge concerning granular materials employed in pavement structures is limited. In addition, to date, no general framework has been established to explain and evaluate satisfactorily the behavior of unbound granular materials under the complex repeated loading which they experience.This thesis presents a packing theory-based framework to evaluate the mechanical properties of unbound granular materials. The framework was developed based on the particle-to-particle contact, the particle size distribution and the packing arrangement. The skeleton of the unbound materials should be composed of both coarse enough particles and a limited amount of fine granular materials to effectively resist deformation and carry traffic loads. Based on this, the framework identifies the two basic components of unbound granular materials, namely the primary structure (PS) - a range of interactive coarse grain sizes that forms the main load carrying network in granular materials and the secondary structure (SS) - a range of grain sizes smaller than the PS providing stability to the aggregate skeleton.In the framework, disruption potential (DP), PS porosity, PS coordination number and void ratio of skeleton (PS+SS) are among the key packing parameters which were established from the framework. These parameters were validated by evaluating the permanent deformation, resilient modulus and California bearing ratio of unbound granular materials using different materials with various experimental results.Furthermore, in this thesis a new moisture distribution model (Birgisson-Jelagin-Yideti (BJY) moisture distribution model) was introduced. In the model, SS particles associated with water retention. The water is stored as meniscus water between these small particles and fully filled in small voids. The volume of meniscus water between SS particles and the measured matric suction values are the two key parameters considered in the model. The results showed that the model developed is capable of predicting the experimentally measured matric suction values for a range of gradations.Finally, the application of shakedown and packing theories to characterize permanent deformation behaviour of unbound aggregate materials is presented. A simple finite element analysis has also been simulated in order to find out the effect of disruption potential on the shakedown limit load. Experimental results were used for the simulation of the finite element and compared favourably with the predicted mean stress and dimensionless shakedown load using DP values.