Keywords: pavement analysis, flexible pavement, finite element, cyclic loading, non-linear, ABAQUS.

Mechanistic methods based on multi-layer elastic theory are used for the design of flexible pavements. In these methods, all pavement layers are assumed as homogeneous, linear elastic and isotropic and the loading is considered as static. However, in reality, pavement layers behave far from these ideal conditions. Research is being carried out to incorporate the real conditions of the pavement layers combined with dynamic and cyclic loading in the analysis of flexible pavements, using the finite element theory. A research study has been undertaken herein in this direction and is being presented in this paper. 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. A pavement section where ALF (Accelerated Loading Facility) trial has been carried out at Callington-South Australia (Site No 5 of ALF trial at Callington) [1], is selected for this study. The reason for selecting ARRB's (Australian Road Research Board) accelerated loading facility is its capability of applying a cyclic loading on pavement structures. This selected pavement structure is modelled as a finite element model, and analysis has been carried out using the finite element computer package ABAQUS/STANDARD [2].

At the selected 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. Therefore, the behaviour of new asphalt layers can be considered as linear and the existing granular layers can be considered as non-linear. A pavement section consisting of six pavement layers with thicknesses conforming to thicknesses given in [1] and an infinite subgrade, is modelled as a finite element model.

The results of field and laboratory tests carried out during the ALF trial are given in reference [3]. In estimating the linear properties of pavement materials, those test results are used together with AASHTO Road Guide [4]. In estimating the non- linear properties of granular materials, results published in the research report [5] are used. This report presents the results of repeated load triaxial tests carried out on soils collected from two South Australian borrow pits. The k-theta model [6] is used for modelling non-linear characteristics of granular materials.

During ALF trial, 80kN load has been applied through a dual wheel assembly, with a unidirectional trafficking speed of 20km/h. The 40kN wheel load is assumed to be uniformly distributed over the contact area between tyre and pavement. The size of contact area depends on the contact pressure. The contact pressure is assumed as equal to the tyre pressure. Tyre pressure is equal to 700 kPa, as given in [1]. The contact area can be represented by two semicircles and a rectangle [7]. Further, this shape of two semicircles and a rectangle is converted to a rectangle having an area of 0.5227 and a width of 0.6. Since =0.330m, the contact area has the dimensions of 0.288m 0.198m.

In ABAQUS this pavement block is modelled with C3D27R (Continuum 3- Dimensional 27 node elements with reduced integration) brick elements. C3D27R element type is quadratic. Quadratic elements yield better solution than linear interpolation elements [8].

The analysis is carried out when this modelled pavement, is subjected to a static and cyclic loading. Asphalt layers were assumed as linear elastic. Granular layers were assumed as linear initially and non-linear later. The results indicate that displacements under cyclic loading when non-linear materials are present, are the closest to field measured deflections.

1

P. Kadar, "The Performance of Overlay Treatments and Modified Binders Under Accelerated Full-Scale Loading-The Callington ALF Trial", Research Report ARR198, Australian Road Research Board, Victoria, Australia, 1991.

2

ABAQUS Version 5.7, User's Manual, Hibbitt, Karison, Sorenson, Inc., Pawtuckett, U.S.A.,1997.

3

J. E. Statton, G.W. Evans, "Callington ALF Trial. Progress Report 4", Report No. MS41-4, Highways Department, South Australia, 1989.

4

AASHTO Guide to Design of Pavement Structures, American Association of State Highway and Transportation Officials, Washington D.C., 1993.

5

M.G. Symons, D.C. Poli, "Stabilisation of Pavement Soils from South Australia",. A research report. Structural Materials and Assemblies Group, University of South Australia, 1996.

6

R.G. Hicks, C.L. Monismith, "Factors Influencing the Resilient Properties of Granular Materials", Highway Research Record 345, Highway Research Board, Washington D.C.,15-31, 1971.

7

H.Y. Huang, "Pavement Analysis and Design", Prentice-Hall Inc., 1993.

8

C. Kuo, K.T. Hall, M.I. Darter, "Three-Dimensional Finite Element Model for Analysis of Concrete Pavement Support", Transportation Research Record 1505, Transportation Research Board, National Research Council, Washington D.C., 119-127,1995.

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