Non-linear finite element analysis of flexible pavements Muhammad N.S. Hadi * , B.C. Bodhinayake Faculty of Engineering, University of Wollongong, Wollongong, NSW 2522, Australia Abstract A research study is being undertaken to incorporate the realistic material properties of the pavement layers and the moving traffic load, in the analysis of flexible pavements, using the finite element theory. As a preliminary step taken herein in this direction, a pavement structure where field measurements have been carried out when subjected to a cyclic loading, is selected and modelled as a finite element model. The analysis is being carried out using the finite element computer package ABAQUS/STANDARD, when this pavement model is subjected to static and cyclic loading while considering the linear and non-linear material properties of the pavement layers. The results indicate that displacements under cyclic loading when non-linear materials are present, are the closest to field measured deflections. q 2003 Elsevier Ltd. All rights reserved. Keywords: Pavement analysis; Flexible pavement; Finite element; Cyclic loading; Non-linear; ABAQUS 1. Introduction In mechanistic methods used in the analysis of layered pavement systems under traffic load, the pavement layers are considered as homogenous, linear elastic and isotropic and the loading is considered as static [1]. These mechan- istic methods work reasonably well, if the pavement subgrade system behaves as a linear elastic system [2]. The use of multi-layer elastic theory together with static loading is a rational approach compared with older empirical pavement design methods. However, in the real situation, these heterogeneous pavement layers behave far from these ideal conditions and are subjected to dynamic and cyclic loading. Researchers diverted their research to the finite element method, which provides a better solution in the dynamic analysis of pavements while considering the heterogeneity, non-linearity and orthotropy condition of the pavement structure at the same time [3,4]. With the availability of high-speed computers, finite element methods are gaining acceptance as the finite element analysis programs can handle complex geometry, boundary conditions and material properties with ease [5]. But still these research efforts are in their early stages. Research is being undertaken to model the flexible pavement as a finite element model, with defined boundary conditions and to investigate the effects of static and cyclic loading when combined with linear and non-linear characteristics of pavement materials, in the analysis of flexible pavements. A pavement section where Accelerated Loading Facility (ALF) trial has been carried out at Callington, South Australia (Site No. 5 of ALF trial at Callington), is selected for this study [6]. The reason for selecting Australian Road Research Board (ARRB’s) accelerated loading facility is its capability of applying a cyclic loading on pavement structure. At this site the existing cracked asphalt surface course and granular base course have been removed and replaced with two new asphalt layers before the ALF trial, so that the behaviour of the new asphalt layers can be considered as linear and the granular layers below the new asphalt layers can be considered as non-linear. 2. Background Design methods for flexible pavements have evolved since the turn of the last century. Empirical methods with or without a strength test were the early methods employed in the design of flexible pavements. The method without strength test refers to the soil classification system provided by Hogentogler and Terzaghi [7]. In the method with strength test the thickness of pavement was related to CBR [8]. By 1950, two methods based on limited deflections and limited shear failure were presented. The method based on limited deflection was presented by Kansas State Highway Commission [9]. The method based on limited shear failure was first presented by Barber [10] and later by McLeod [11]. 0965-9978/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0965-9978(03)00109-1 Advances in Engineering Software 34 (2003) 657–662 www.elsevier.com/locate/advengsoft * Corresponding author. Tel.: þ 61-2-4221-4762; fax: þ61-2-4221-3238. E-mail address: mhadi@uow.edu.au (M.N.S. Hadi).