Enhanced Attenuation of Train-Induced Vibrations in Metro Superstructures via Radial Metastructures Embedded in Trackbeds

As urban density increases with more buildings constructed above complex metro transportation lines, the metro systems are characterized by higher speeds, increased line density, increased travel frequency, and sometimes shallow burial depths. The severe vibrations induced by metro operations significantly affect the life quality of residents. Traditional vibration attenuation structures, such as active measures (e.g. floating slabs and resilient rail pads) and passive methods (e.g. open trenches and soft-filled barriers), often fall short in addressing low-frequency vibrations and are limited in scalability. This paper introduces a novel approach using metamaterials with unique properties that can be engineered to cater for specific needs. It presents the design and evaluation of a radially periodic vibration-attenuation structure embedded within metro trackbeds, termed a metastructure barrier. This barrier consists of alternating layers of two materials arranged in a periodic pattern. The theoretical dispersion relation to identify the bandgaps is derived using transfer matrix method (TMM) and spectra element method (SEM), followed by finite element simulations to evaluate efficacy of the structure in attenuating vertical ground vibrations. The result indicates a substantial reduction in radial wave transmission within the 0–400[Formula: see text]Hz range, particularly effective at 0–100[Formula: see text]Hz, which is the target design frequency. Additionally, the paper considers practical aspects such as a hybrid structure incorporating another two floating slab track types, and the desirable number of layers in the barrier design for real-world scenarios. By applying the vibration data from a specific section of Beijing Subway, effectiveness of this metastructure is confirmed. With its customizable design and robust vibration attenuation capabilities, this metastructure offers a promising solution for mitigating train-induced vibrations in both metro renovation and new urban construction projects.