Surface waves in a stratified half space with enhanced continuum properties. Part 2: Analysis of the wave characteristics in regard to high-speed railway tracks

This paper discusses the propagation of surface waves in a stratified half space, which consists of an elastic granular upper layer that rests on a ha lf-infinite elastic substratum. For the upper layer the effect of particle translation and particle rotation are incorporated via a second-gradient co ntinuum formulation and a Cosserat continuum formulation, respectively. Con sequently, additional surface wave modes emerge, which cannot be described by a classic elastic formulation. After a general discussion of the surface wave dispersion curves, the critical behaviour of the stratified medium un der a moving vibrating load will be examined. Here, the adjective 'critical ' designates that the wave energy that is generated by the moving road has the same velocity as the load itself, which results in resonance phenomena. The model parameters in this study are chosen to be representative for con ditions in a high-speed railway track. The critical load Velocities will be determined for several cases, where the effect by the ballast particle siz e, the ballast layer thickness, the load velocity and the sleeper distance will be analysed. (C) 1999 Editions scientifiques et medicales Elsevier SAS .