FOCUSING OF GROUND VIBRATIONS GENERATED BY TRANS-RAYLEIGH TRAINS TRAVELLING WITH ACCELERATION

Over the last two decades, high-speed railways have been developed rapidly in many countries. The main reason for that is that they make a viable alternative to air transportation for short and medium distances, and they produce very low air pollution per passenger. However, as many other means of transportation, high-speed railways are not free of environmental problems. In particular, ground vibrations generated by high-speed railways is one of the major environmental problems that must be mitigated to allow high-speed trains to be used in densely populated areas1. The intensity of railway-generated ground vibrations generally becomes larger at higher train speeds. For modern high-speed trains the increase in generated ground vibrations is especially large when train speeds approach certain critical velocities of elastic waves propagating in a trackground system. The most important of them is the velocity of Rayleigh surface wave in the supporting ground. As was theoretically predicted more than twenty years ago2-4, if a train speed v exceeds the Rayleigh wave velocity cR in supporting soil, the phenomenon of ground vibration boom occurs. This phenomenon is similar to a sonic boom for aircraft crossing the sound barrier, and it is usually associated with a very large increase in generated ground vibrations, as compared to the case of conventional trains. The existence of ground vibration boom has been later confirmed experimentally5,6. Therefore, it is now possible to speak of 'superseismic' or, more precisely, 'transRayleigh' trains7-9 in the same way as people speak of supersonic aircraft. The increased attention to the problems of ground vibrations associated with high-speed trains is reflected in a growing number of theoretical and experimental investigations in this area (see e.g. Refs. 1,10-14).