Track bed stability is of major importance for the safety and comfort of rail traffic. Quasi-static and dynamic loads from train-traffic are applied to the entire track system: superstructure, substructure and subsoil. Owing to the dynamic loads on the track system and lack of maintenance of the track bed, an accumulation of excess pore water pressure can develop within the substructure. Furthermore, a pumping effect exerted on the track system, which depends on the axle load and velocity of the vehicle, may cause in mud hole formation, rising of the underlying soil, ballast contamination and the clogging of gravel bed pores. Consequently, the subgrade resistance is reduced and hence the system loading capacity. The main objective is to detect mud holes, as early as possible, by non-invasive, nondestructive measurements. The plastic deformation induced by the development of the mud holes is investigated by simulating the complex track-subsoil interaction with the finite element method (FEM). In this analysis, the advanced hypoplastic model has been used. More focus will be paid on the effect of the boundary condition on the dynamic wave propagation. For this purpose, a one-dimensional problem is investigated. The time-dependent problem is studied next by considering the real load history of the rail traffic.
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