High-speed trains (HST) bring about special problems compared to typical freight and passenger trains. These special problems include the train passing the Rayleigh wave barrier and associated large deformations, particularly when the HST travels on soft soils. Results from instrumented tests performed with an HST on soft soil at different sites and associated numerical analyses have indicated that a large dynamic amplification appears in the vertical dynamic movement of the high-speed railways (HSR) as the train speed approaches the Rayleigh wave speed; this is attributed to a resonance phenomenon. This Rayleigh wave speed is the equivalent Rayleigh wave speed of the rail/embankment/ground system. This threshold speed is called the Critical Speed and is known as Ground Mach 1 or GM1. The question is to quantify this dynamic amplification to be in a better position to decide if it can create some serious ride discomfort or even derailment. A 4-D finite element model, developed in LS-DYNA, was used to simulate this problem. The model included the full train length and the raised embankment. The results of this study show that the Critical Speed is controlled by the Rayleigh wave velocity of the subsoil and that the maximum deflection occurring at the Critical Speed is about three times larger than the static deflection.
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