Geodynamics of very high speed transport systems

Abstract

This work reveals the existence of a new dynamic load amplification mechanism due to ground surface loads. It is caused by the interaction between a moving vehicle's axle configuration and the vibration characteristics of the underlying soil-guideway system. It is more dominant than the traditionally considered 'critical velocity' dynamic amplification mechanism of the guidewayground structure, and is of relevance to very high speed transport systems such as high speed rail. To demonstrate the new amplification mechanism, first a numerical model is developed, capable of simulating ground-wave propagation in the presence of a series of discrete high speed loads moving on a soil-guideway system. The model couples analytical equations for the transportation system guideway with the thin-layer element method for ground simulation. As a practical example, it is validated using high speed railroad field data and then used to analyse the response of a generalised single moving load at high speed. Next the effect of multiple discrete vehicle-guideway contact points is studied and it is shown that dynamic amplification is highly sensitive to load spacing when the speed is greater than the critical velocity. In particular, large resonant effects occur when the axle/magnet loading frequency and the propagating wave vibration frequency of the soil-guideway structure are equivalent. As an example, it is shown that for an individual case, although critical velocity might increase displacements by 50-100%, for the same scenario, axle configuration can increase displacements by 400%. It is also shown that resonance is sensitive to the total number of loading points and the individual frequencies excited by various spacings. The findings are important for current (e.g. high speed railway) and potential future (e.g. hyperloop) transport systems required to operate at speeds either close-to, or greater than the critical velocity of their supporting guideway-soil structure. In such situations, it is important to design the vehicle and supporting structure(s) as a combined system, rather than in isolation.

High speed railway ground dynamics: a multi-model analysis

“…When the soil stiffness is soft, track and ground displacements return to their equilibrium position more slowly than when the soil is stiff. Similarly, when approaching critical velocity, the deflection bowls below wheels elongate, and wheels that are closely spaced experience superpositionthis has been observed both numerically and in field data [16,46]. Constructive interference is shown in Figure 11 for a 2-axle load moving at critical velocity on both a homogenous and bedrock supported soil.…”

“…Although it is rare for trains to operate above critical velocity, in such a case, it should also be noted that resonance can occur due to coincidence between axle spacing wavelength and the free-vibration wavelength of the track-ground structure [46]. This constructive interference is evident in Figure 11b where the free-vibration wavelength and vehicle axle spacing are both equal.…”

Railway ground vibration and mitigation measures: benchmarking of best practices

“…In general, when the train speed is approaching the Rayleigh wave speed of the transmission path it is possible to have considerable growth in the track vibration and consequently an increase in the ground-borne effects [98,99] as in the case of the aforementioned Ledsgard project. Experimental demonstration of these effects has been redrawn for three sites located in Sweden, UK and Netherlands, by Connolly et al [64,100] as depicted in Fig.…”

Differential Settlement and Dynamic Load Effects across Lime Treated Rail Transition Zones

“…Rayleigh waves) alongside the elastic loading of the trackbed system from repeated very short term, but significant magnitude axle loading from the HS train. This modelling considers only the movement caused by the Rayleigh waves and fundamentally it is expected that stiffer subgrade will permit surface waves to move faster through the ground, to cause less wave resonance and therefore less rail level movements [18].…”