Study On Vibration Isolation Effect Of Combined Vibration Isolation Barrier

Urban mass transit develops rapidly in China.It has important scientific significance and practical value to effectively reduce the environmental vibration caused by subway train operation.According to the generation mechanism and propagation process of traininduced vibrations,the control measures are mainly divided into 3 categories,namely the measures in the vibration source,in the propagation path and around the vibration subject.There have been many research results and application cases about measures in the vibration source,but the cases of vibration isolation barriers are rare.Most of the relevant studies are theoretical research and numerical modelling,and the research results are few.As an indispensable part of comprehensive vibration reduction measures,vibration isolation in propagation path is of great engineering significance and practical value.In this paper,addressing the research of damping materials,the composite vibration isolation barrier is studied systematically and deeply using numerical simulation and laboratory test.The main research work and achievements are as follows:1.The composite vibration isolation barriers of rigid materials and flexible materials are taken as the research objects.The dynamic characteristics and vibration isolation effects of 4 types,indicated by AB,BA,ABA and BAB respectively are studied by numerical simulation.In this context,A represents rigid concrete material,B represents flexible polyurethane material.The results show that the 3-layer composite vibration isolation barrier has better vibration isolation capacity than that of the single-layer and 2-layer ones.Moreover,the BAB type,that is,the Polyurethane-Concrete-Polyurethane composite vibration isolation barrier has the best effect.According to this,4 working conditions are determined for laboratory test,namely,1)no vibration isolation barrier,2)single concrete vibration isolation barrier(A),3)Concrete-Polyurethane-Concrete composite vibration isolation barrier(ABA)and 4)Polyurethane-Concrete-Polyurethane composite vibration isolation barrier(BAB).2.The preparation of the dynamic test is carried out,including the design of working conditions and the measuring points.In the tests,3 vibration isolation conditions and one reference condition without isolation measure are considered.And the buried depth of vibration source is 0 m,0.2 m,0.4 m,0.6 m and 0.8 m,respectively.So a total of 20 test conditions are designed.The dynamic test system is carried out on the multifunctional dynamic test platform of Beijing Jiaotong University,including sandboxsoil modular,excitation modular,vibration picking modular,vibration isolation modular and signal processing modular.The materials used to make the barrier model are as follows: the rigid PVC plate is used to simulate concrete,and the polyurethane is used as the flexible material.The test models are made according to the recommended working conditions and the material parameters are measured.3.The dynamic tests of vibration isolation barriers are carried out using the designed system.By analyzing vibration acceleration peak value on the vibration received area and insertion loss of Z vibration level,comparative studies between the composite vibration isolation barriers and the single-material barrier are carried out.The dynamic performance and the vibration isolation effect are obtained as well.And the effect on different embedded depth of the vibration source is studied.It is concluded that the best type is the BAB,that is,Polyurethane–Rigid PVC–Polyurethane combined vibration isolation barrier.This provides reference for subsequent numerical simulation.4.Based on an actual project of Beijing Metro Line 6 between Liaogongzhuang station and Xihuangcun Station,a three-dimensional dynamic numerical model of railtunnel-soil was established using ABAQUS,and the dynamic performance and vibration isolation effect of composite vibration isolation barrier of flexible-rigid-flexible material(BAB)subject to train load was analyzed.The impacting characteristics of 4 factors,including the buried depth of the barrier,the thickness of the rigid material,the thickness of the flexible material and the distance between the barrier and the vibration source,are further studied.Based on this,the optimized design of the vibration isolation of the barrier is carried out.The vibration reduction effects of two measures are analyzed,namely the forementioned BAB type composite vibration isolation barrier and rubber-concrete vibration isolation roadbed.The combined and separated application of this two measures are analyzed,which can provide reference for rail transit vibration reduction design.