Study On Periodic Piles For The Isolation Of Train-Induced Environmental Vibration Based On Band Gap Theory

The problem of environmental vibration induced by rail transit operation is becoming more and more prominent.When the vibration reduction measures at the vibration source are taken to extreme,still unable to alleviate the problem,or track vibration mitigation measures can not be taken,the transmission mitigation measures sometimes can be an inevitable choice.Due to the elastic wave band gap nature of the periodic structures,vibration isolation of the characteristic frequency range can be realized by adjusting the structural forms and material composition to design the band gap.Therefore,in this paper,the periodic piles are introduced into the vibration propagation path of rail transit,and considering its band gap characteristics,the ambient vibration isolation of significant frequency range induced by rail transit is performed.In this context,a systematic and in-depth study has been carried out by means combinated with theoretical analysis,numerical simulation and experimental tests focusing on the main factors influencing the band gap distribution of periodic piles and the related scientific issues that need to be solved urgently for the application of periodic piles in the field of vibration isolation in rail transit,based on the band gap theory of periodic structures,with the support of Fundamental Research Funds for the Central Universities named"Application researches of periodic piles on vibration isolation by transmission mitigation measures in rail transit"(No.2017YJS153),“Researches on vibration isolation by transmission mitigation measures in a metro depot”(No.2016JBM040).The main research contents and results and the main innovations include:(1)A compositive dynamics experimental platform simulating underground structures is designed and constructed independently,and the principle test of attenuation zone is carried out which verifies the effectiveness and practicability of the band gap theory in vibration isolation design of periodic piles.The vertical and horizontal attenuation zone distributions of hollow steel piles with the hexagonal lattice arrangement,hollow steel piles embedded and filled with soil with the hexagonal lattice arrangement,hollow steel piles with the square lattice arrangement and hollow steel piles embedded and filled with soil with the square lattice arrangement are gained.The effects of lattice forms,soil embeding and filling,and other factors on the isolation efficiency and attenuation zone are achieved.The experimental results of the attenuation zone show good accordance with the calculation results of the band gap.(2)The influence of geometric configuration and material composition on the band gap distribution of periodic piles is studied.Three new types of piles for vibration isolation are proposed,including honeycomb piles,cross-bonding piles and type X piles,besides conventional pile forms of circular and square section.Through the analysis of the influencing factors,the change rules of geometric configuration parameters on the band gap distribution,such as periodic constant,filling rate,control size m/n/p/q/a,etc.,are mastered.It is found that they have more complex configuration parameters and more abundant band gap regulative capability.The study provids a reference for the optimal selection of the three new types of periodic structures.(3)A new evaluation index for band gap performance of periodic piles(Band Gap Performance Evaluation Function ?)is proposed,which considers multiple factors such as the width of band gap(lower bound frequency and upper bound frequency)and center frequency,is a single evaluation index.This index also evaded the uncertainty caused by multi index analysis.The initial band gap is no longer used as the only basis for selection and all the distribution of the band gaps in the frequency range of interest is fully considered.(4)By introducing frequency domain characteristics of environmental vibration in rail transit into Band Gap Performance Evaluation Function 0,the selection method of periodic piles for the vibration isolation of the characteristic frequency range in rail transit is established,which provides a basis for structural design.(5)In a specific case,through numerical simulation and orthogonal analysis,the impacts of row number,column number,pile length,vibration source depth and distance between periodic piles and the vibration source on the spatial distribution and attenuation level of attenuation zone of finite periodic pile structures are obtained.Taking the evaluation index ER at the center frequency of the initial band gap of finite periodic piles as evaluation quantity of the orthogonal analysis,the spatial distribution and attenuation level of the attenuation zone are comprehensively evaluated,so as to obtain the primary and secondary order and relevance of each single influcing factor on the damping effect of the attenuation zone,and provide a basis for the selection and design of engineering periodic piles.The results show that the primary and secondary order of the influencing factors on the vertical damping effect of the attenuation zone is:vibration source depth>pile length,row number>column number>distance between periodic piles and vibration source;the primary and secondary order of the influencing factors on the horizontal damping effect of the attenuation zone is:distance between periodic piles and vibration source>vibration source depth,row number>pile length>column number.