DEM simulation of triaxial tests of railway ballast fouled with desert sand
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Some high-speed rail lines go through desert zones where sand particles transported by winds may foul track ballast layers. This fouling can be troublesome since it increases the stiffness of the layer and reduces its capacity to absorb vibrations from the rolling stock. We are studying this phenomenon through both laboratory and numerical experiments. In the laboratory, we performed two kinds of experiments: 9 inches triaxial tests and physical modelling in the CEDEX Track Box testing facility. The latter is a unique 1:1 model of railway track section (of dimensions 21 m ×5 m ×4 m) that has been built to model high-speed rail lines (with passenger and freight trains passing at velocities of up to 400 km/h). The laboratory experiments allowed us to measure the change of stiffness with the fouling level (represented through the void contaminant index, VCI). Numerical simulations are being performed with the Discrete Element Method, reproducing drained triaxial test conditions. Due to the considerable different size of railway ballast and sand grains, we are using idealized packings of spherical particles to study this phenomenon. We are paying particular attention to the sample size effects and are registering the evolution of the stiffness with the fouling level up to high values of VCI. The results obtained from these idealized systems will be contrasted to the laboratory experiments carried out with real railway ballast and sand.