Analytical Study On The Isolation Mechanism Of Metamaterials For Traffic-induced Environmental Vibrations

Transportation infrastructures,with rapid development,have greatly facilitated the lives of people,while their operations may cause damages to adjacent buildings,harm the physical and mental health of residents,leading to increasingly serious problems of environmental vibrations.Traditional measures are usually not efficient for mitigating far-field ground-borne vibrations.Therefore,with great engineering significance and social value,it is important to design novel isolation measures for traffic-induced environmental vibrations.Environmental vibration control is essentially the manipulation of elastic waves,metamaterials improve the dispersion properties of host medium to manipulate elastic waves.In recent years,benefiting from peculiar manipulation mechanism of elastic waves,metamaterials have provided opportunities to design novel measures for mitigating traffic-induced environmental vibrations.Considering random and broadband characteristics of elastic waves induced by traffic loads,this study proposes novel metamaterials capable of mitigating traffic-induced environmental vibrations.Meanwhile,in the context of elastodynamics,this study also develops analytical models able to capture the dynamic interactions between traffic-induced elastic waves and novel metamaterials.Main research work is summarized as follows:(1)To consider the effect of random traffic loads on the ground vibration,based on the pseudo excitation method(PEM),this study develops an analytical model to investigate the nonstationary responses of a three–dimensional tunnel–soil system subjected to moving stochastic loads.The influence of the soil stiffness and tunnel lining on the stochastic response of the saturated soil is investigated.Then,to consider the effect of soil parameter uncertainty on the ground vibration,with the aid of the Monte Carlo simulation(MCS)and a prediction model of train-induced vibrations,this study also develops an efficient model of stochastic ground-borne vibrations considering the uncertainty of soil parameters.The probability of the traffic-induced ground vibrations exceeding the limit can be reasonably eveluated.(2)Aiming at the broadband characteristics of traffic-induced vibrations,this study proposes a novel kind of buried metabarrier realized by an array of mass-spring-dashpot resonators encased into flexible pipes.This novel metabarrier can create not only the resonance-type bandgap within relatively low frequency range,but also the Bragg-type bandgap covering higher frequencies,achieving the broadband mitigation of traffic-induced environmental vibrations.Meanwhile,with the aid of the wave function method and multiple scattering theory,an analytical formulation is developed to model the interaction between the tunnel-radiated waves and metabarrier-scattered waves.The first case focuses on the mitigation performance of a single-unit metabarrier,investigating the local resonance behavior of the single resonant unit as well as reveal the effects of geometric dimension of metabarrier unit on the resonance bandgap.The second case of the multiple-units metabarrier investigates the coexistence mechanism of Bragg-type bandgaps(from geometric scatterings of periodic pipes)and resonance-type bandgaps(from local resonances of resonators),as well as demonstrates the combined bandgaps.(3)This study proposes a novel tunable metasurfaces capable of shielding anti-plane polarized Love waves excited traffic loads.Also,with the aid of the multiple scattering theory,an analytical formulation is originally developed to investigate the interplay between Love waves and the tunable metasurface.Besides,a closed–form dispersion relation governing the hybrid Love waves is derived by utilizing the effective medium approximation.The modelling capabilities of the proposed analytical formulation are demonstrated through the detailed investigation on the interaction between Love waves and a pair of resonators and a finite-size metasurface.By inspecting the dispersion relation,mode shapes and full wavefield,this study investigates the hybridization features between the metasurface resonances and different Love modes,and reveals the manipulation mechanism of the proposed metasurfaces.The hybridization between the metasurface and fundamental Love mode can create a bandgap,leading to the surface-to-bulk wave conversion.While the second Love mode is hybridized as another surface wave mode,leading to the disappearance of Love wave bandgap.(4)Aiming at traffic-induced structure-borne vibrations,this study proposes a novel locally resonant periodic foundation(LRPF)by introducing the negative-stiffness vibration absorbers,and develops an analytical model to investigate its mitigation performance.A tunnel–ground–LRPF–superstructure coupled model is developed by combining the tunnel–ground and LRPF–superstructure systems,and dynamic interactions between them are investigated.The proposed LRPF exhibits a broad bandgap covering the ultra–low frequencies and the eigenfrequencies of the LRPF–superstructure system,resulting in significant attenuation effects on the structure–borne vibrations.The influence of the tunnel–ground–LRPF interaction on the mitigation performance of the LRPF is revealed.The flexible support provided by the ground can change the boundary conditions of periodic structures,leading to additional resonance frequencies of the LRPF–superstructure system.Besides,the presence of tunnel can affect the mitigation efficiency of the LRPF in the attenuation zone.