Research On Application Of Periodic Piles In Vibration Isolation Of Rail Transit

With the rapid development of urban mass transit in China,environmental vibration influence induced by metro system operation is becoming increasingly prominent.When replacing ordinary track to the vibration-danping track and adding the vibration-isolating support to the sensitive building is infeasible,or when the track vibration-danping measures alone cannot solve the increasingly significant environmental vibration problem,the transmission mitigation measures can be a necessary way to solve the problem Vibration waves in the band frequency gap can not propagate through the periodic structure,because of the elastic wave band gap characteristics.In this paper,the piles in the transmission mitigation measures are periodically designed to prevent the propagation of elastic waves in a specific band frequency gap,thereby protecting the sensitive building from vibration Based on the above research background,with the sipport of the project "Researches on vibrationisolation by transmission mitigation measures in a metro depot"(No.2016JBM040)and "Application researches of periodic piles on vibration isolation by transmission mitigation measures in rail transit"(No.2017YJS153),which are funded by the Central University Basic Research Business Expenses,research on key scientific and technical issues involved inperiodic vibration isolation of rail transit characteristic bands is carried out by the principle experiment amd numerical simulation.The main works are as follows:1、The principle experiment of periodic piles vibration isolation was designed and carried out for expforing the actual attenuation effect and vibration isolation performance of the periodic piles in the theoretical calculated band gaps.There are five experimental cases including hollow steel piles with the triangular lattice arrangement,hollow steel piles filled with soil with the triangular lattice arrangement,hollow steel piles with the square lattice arrangement,hollow steel piles filled with soil with the square lattice arrangement and no piles.The acceleration amplitude reduction factors ARF are calculated by the dynamic response of the soil with vibration isolation piles and no pile.The attenuation zones(AZ)are obtained further and compared with the band of frequency gaps(BFGs).The result shows that the measured vibration response has been greatly attenuated within the band gaps and the level of attenuation is all above 47%and up to 98%,the actual attenuation effect is obviovis,and the vibration isolation performance is outstandin.2、For carrying out the experiment successfully,a series of preliminary preparations and trial work are eonducted including determining the type of the model box,the boundary material,the various indicators of soil(sunch as gradation,density,water content,wave velocity,etc).3、Taking the environmental vibration influence induced by underground mass transit as the research background,according to the requirement of vibration isolation target,based on the periodic structure band gap theory,the design parameters of the vibration isolation piles are proposed and verified by numerical calculation.The tunnel-stratum-piles model and the tunnel-stratigraphic model were established using MIDAS GTS and obtain the attenuation zone of the designed piles.Comparing the attenuation zone and the band of frequency gap and the result shows that the calculated vibration response has been greatly attenuated within the band gaps.The vibration isolation effect of the periodic piles is analyzed from acceleration amplitude reduction factor ARF and one-third octave insertion loss IL(fi).