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This research paper deals with experimental characterisation and numerical modelling of the resilient behaviour of Unbound Granular Materials (UGMs) usually used in road construction. The first part of this paper describes the main results of an experimental program that was carried out to assess the mechanical properties of two local Unbound Granular Materials (UGMs) for construction purposes in road pavement. The second part of this paper is devoted to the numerical modelling of the resilient behaviour of UGMs used in flexible pavements. For this purpose, several nonlinear unbound aggregates constitutive models are implemented within an axi-symmetric finite element code developed to simulate the nonlinear behaviour of pavement structures. In addition, deflection data collected by Falling Weight Deflectometer (FWD) are incorporated into the analysis in order to assess the sensitivity of critical pavement design criteria and pavement design life to the constitutive models. Finally, conclusions of engineering significance are formulated.

Current engineering practice pays little attention, if any, to nonlinear abutment-backfill soil interaction (ABSI) effects on seismic behaviour of bridges. The primary focus of this article is to assess the influence of ABSI on the progressive seismic failure of bridge structures. Emphasis is placed on the significance of ABSI effects, including abutment behaviour and backfill soil flexibility. Nonlinear dynamic analysis is performed using a bilinear hysteretic model for the bridge superstructure and nonlinear characteristics of the expansion joint. Results indicate that ABSI has a significant effect on the seismic response in the longitudinal direction and can effectively reduce bridge seismic demands. ABSI affects rotational ductility demand at pier ends of the bridges, relative displacements, pounding and axial forces in the restrainers. Thus, it is essential that numerical models used in seismic assessment of bridge structures properly consider abutment-backfill interaction.Keywords: Abutment-backfill soil interaction, highway bridges, nonlinear dynamic analysis, seismic failure.HIGHWAY bridges represent structures of economic and strategic importance. They are generally built in reinforced or prestressed concrete to span over a valley, river, road or any physical obstacle to essentially allow the passage of all kinds of vehicles. High seismic performance is usually required for this special category of structures, the potential collapse of which can result an significant economic impact.Abutment modelling and behaviour 1 , soil conditions and foundation soil stiffness 2 , soil structure interaction 3 and embankment flexibility 4 have been found to significantly influence the response of bridge systems and eventually their seismic failure 5 under strong ground motions. In addition, analysis of past and recent bridge damage data has illustrated that seismic participation of bridge abutment and backfill soil can lead to cost-effective design of bridges 6 . The primary focus of this article is to assess the influence of abutment-backfill soil interaction (ABSI) on the progressive seismic failure of bridge structures. Emphasis is placed on the significance of ABSI effects, including abutment behaviour and flexibility of backfill soil at the abutments. The effective stiffness, foundation soil damping and capacity parameters at the base of the spread footings have been evaluated using FEMA procedures 7 . Yields strengths of abutment backfill in compression and in tension have been evaluated using Mononobe-Okabe pseudostatic approach for passive force and frictional sliding capacity at the abutment footing respectively. Nonlinear dynamic analysis is performed using a bilinear hysteretic model for the bridge superstructure and nonlinear characteristics of the expansion joint. Based on the results obtained in the present study, it is concluded that ABSI has significant influence on seismic demands of bridge systems and hence can lead to cost-effective design of bridge structures. However, special attention should be ...

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