On site mechanical characterization of the ballast state

Abstract

Ballast is a major railway component whose behaviour is still not sufficiently controlled. The identification of mechanisms leading to track ageing is difficult to achieve as the process occurs over several years at particle scale. Models Context and purposesBallast is an important railway component whose behaviour is still not sufficiently controlled. Identifying the mechanisms leading to track ageing is difficult since the process occurs over several years at particle scale. Periodic monitoring of railway track provides indications on track geometry and allows identifying defects [14,16,28]. However, these data do not allow diagnosing ballast state.Several experimental and numerical studies have been carried out in order to better understand track behaviour and study the problems related to relative settlement or carry out maintenance.These experimental studies were carried out to better understand railway settlement under cyclic stress and characterize ballast behaviour. By using a test bench with ballast at 1/3 scale, Bodin and Guerin [6,13] proposed settlement laws while Al Shaer [3] highlighted ballast fluidification for certain stresses. Lim [17,18] and Indraratna [14] characterized ballast degradation and proposed indicators to qualify the degree of ballast pollution.Numerical studies have highlighted that continuous modelling of the ballast was perfectible. Indeed ballast under sleepers is in a confined environment, thus in a configuration that makes it difficult to reproduce its behaviour by using traditional experimental methods (e.g. triaxial tests).Models have been proposed to take into account ballast characteristics and used to analyze the lateral resistance of a "new" ballast and its behaviour under loading cycles and during tamping [10,17,22,25]. These models based on the discrete elements method provide a description of geometrical and structural modifications of ballast particles through time. To be relevant, these models require reliable and realistic input data and must be validated by site investigations.Among the input parameters necessary for supplying the numerical models the main ones are on-site density, stiffness modulus, geometry and the arrangement of the medium. The goal of this study is to be able to link the ballast's mechanical characteristics at various stages of its life (after deposit, after tamping, after X loadings and at end of lifetime), by using measurements obtained from on-site tests.On site mechanical characterization of the ballast state 31 2011 55 1

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