Influence of Nonlinear Resilient Models of Unbound Aggregates on Analysis and Performance of Road Pavements

Abstract

Proper characterisation of the mechanical properties of unbound granular materials (UGM) is an essential issue in the IntroductionLow to moderate volume roads in Algeria cover more than 70% of the total road network of the country [1]. These road structures typically consist of thin asphalt layers and structurally significant unbound base and sub-base granular layers over subgrade to carry the traffic load. It follows that accurate modelling of granular layer behaviour is of crucial importance for the analysis and prediction of pavement structural performance [2,3].The conventional way of designing a flexible pavement structure in road pavement engineering is to assume a constant stiffness over the granular layer thickness or to derive empirically this stiffness from a rigidity ratio depending on the mechanical properties of the subgrade soil (e.g. [2,4]). However, experimental evidence [5][6][7] shows clearly that the resilient modulus of an unbound granular layer is a non-linear function of the stress levels acting at the various points of the aggregates.Because of this material non-linearity and the sensitivity of the main pavement design criteria to the likely variations of the resilient modulus of the granular layers, numerical simulation of the non-linear mechanical behaviour of unbound granular materials (UGM) need be developed [3,8,9] .Various constitutive models have been developed to this end [7,9]. These resilient models can be categorized into two main classes; the resilient modulus models [6,8,11] and the shearvolumetric strain models [3][4][5]10], frequently used for UGM nonlinear characterization in pavement engineering.In the present study, three nonlinear constitutive models are tested. These are the K -Θ [2, 13], the NCHRP (often called modified universal) [8] and K -G models [3,4]. These models are then implemented within an axi-symmetric FEM code developed herein to evaluate their influence on nonlinear analysis and structural performance of road pavements. The finite element simulation results are validated using FWD backcalculated moduli to predict critical pavement response and design life. In addition, the sensitivity of pavement design criteria and estimated pavement design life to the likely variations of unbound granular material mineralogical nature is assessed and conclusions of engineering significance are formulated.

Evaluation of the Resilient Modulus of the Dunaújváros Loess Soil According to the MEPDG

“…Since the goal was to recreate the regression coefficients as functions of basic soil parameters, grain size distribution and Proctor tests were carried out to determine the soil properties applicable in those equations. The research results that can be found in the literature [5,6] indicate well what are those parameters that are worth trying to assemble such equations, and what is the logic behind the assessment.…”

“…This model is called k 1 -k 3 or universal model in practice, and its main advantage is that it could take into consideration the change of the stress state [4][5][6].…”