Abstract Summary
Among modes of transportation, railway transport has received increasing attention lately especially due to its capability of running fully on electricity, which can be generated from green sources. With the increasing demand on railway transportation, the previously acceptable issues caused by railway transport are quickly turning into challenging problems causing disruptions to the normal operation of traffic. One such an issue is the ground-borne vibration that is changing from a previously localised annoyance to a presently serious societal and economic challenge. Mitigation measures range from interventions at the source level (i.e., vehicle-structure interaction), at the receiver location (e.g., vibration isolating foundations), and on the transmission path. This work is concerned with the last category. More specifically, this study investigates the capabilities of a novel mitigation measure, a so-called metawedge, in reducing the ground-borne vibration at the receiver end. A metawedge is series of barriers (i.e., resonators) arranged periodically in the longitudinal direction and each one is offset with respect to the others in depth direction (i.e., while the first barrier is completely on the surface, the last barrier can be completely embedded). The slight depth difference of each resonator means that each representative cell has slightly different natural frequencies. Consequently, this countermeasure can convert the incoming Rayleigh (surface) waves into body ones, redirecting the energy content deep into the ground. Modelling results show that the metawedge is capable of significantly reducing the vibration levels with as few as five resonators. Furthermore, while conventional single trenches are efficient as mitigation measures only at a certain angle of the incoming waves (outside the critical cone), the metawedge is efficient inside this cone. Although it shows good potential, the results were obtained with unrealistic properties of the individual barriers (heavy steel blocks); therefore, future studies are necessary to design the individual resonator such that it complies with the low frequency requirements of ground-borne vibration of railway transportation. Nonetheless, this study serves as a proof of concept that metamaterials can potentially play an important role in addressing present and future challenges of the railway transportation.
