Abstract : With the deterioration of the railway tracks quicker than estimated at high-speeds, SNCF decided to begin some researches with LCPC. The main aim was to determine the settlement of a railway track, knowing the train speed and the soil composition. The first phase consisted in finding an experimental settlement law related to acceleration in the track. The second phase (my Ph-D thesis) aimed at building a dynamic model to know the vertical acceleration depending on the train speed and on the soil composition. Dynamic approaches were built: first semi-analytical linear multi-layer ones, and then non-linear numerical ones. The comparison between our results and the experimental measures allowed us to sort out some behaviour laws and a railway track model.