Subsoil Vibration Induced By Metro Train Arriving At Or Leaving The Station

With the acceleration of urbanization in China,the urban metro network has become more and more mature,which has greatly reduced the pressure on urban traffic.The travel of the citizens has become convenient and fast,but the series of problems caused by the vibration of the metro train have become more and more prominent.Many research results about the vibration have been achieved in China and abroad.Under special moving conditions,the vibration source characteristics of the metro train arriving at or leaving the station are rich and varied,and the environmental vibration problems induced by it are also complicated and diverse,there is not much research work on this issue,and the results are less reported.This paper attempts to discuss the vibration source characteristics of metro trains under special moving conditions based on wave theory analysis and field test methods.The main research work and results are as follows:1.Research on analysis method of axial excitation vibration source of metro train arriving at or leaving the station.The vibration induced by the metro train arriving at or leaving the station regarded as the axial excitation is acting on the soil layer at the outer edge of subway tunnel structure.For this special excitation,this paper focuses on the analysis of longitudinal vibration caused by track irregularity and axial vibration consistent with the direction of axial excitation.Based on the wave theory,considering the axial excitation changes with the moving time and speed the change of the metro train arriving at or leaving the station,this paper uses the cylindrical wave source that satisfies the wave equation to simulate the train source model.For the longitudinal vibration,the large arc hypothesis is used to solve the reflected wave field coefficient.For axial vibration,the virtual wave source is constructed by using the mirror image principle to solve the reflected wave field coefficient,and the effect of track irregularity is considered.After the expression of the total wave field in the soil layer under the single-line tunnel structure is set,the influence of the double-line tunnel structure on the wave field is further considered.Through the analysis of examples,it is found that double-line tunnel structure has a great influence on vertical vibration.The vertical vibration increases by 26%and the axial vibration increases by 80%from no load to overload condition.2.A spatial vibration source model that satisfied the three-dimensional wave equation is established.The train vibration source which was changing continuously in the time and space domain was converted into a continuous cylinder vibration source in the frequency domain which changed with the running position and the vibration frequency and the incidence Angle.The influence of track irregularity and axial excitation under the moving condition are considered.Through the analysis of the example,it is found that along the moving direction,with the increase of the distance from the station,the surface low-frequency vibration acceleration does not change after the first increase,and the calculation results are compared with the vibration law of the plane wave incident.It is found that the two laws have similarities,and the cylindrical wave source has more abundant spectral characteristics.3.The vibration source test of metro train arriving at or leaving the station is study.The representative ground surface measurement points near xuanwumen station of Beijing metro Line 4 were tested for a long time.The vibration amplitude and spectrum characteristics are analyzed and compared with the calculation results of the spatial vibration source model proposed in this paper.It is found that along the direction of the vertical tunnel,the vibration acceleration amplitude of tests and theoretical results is attenuated as the distance increases,and the trend of the tests and theoretical results is consistent.The variation of the spectral characteristics also results in low frequency.In addition,the test results are compared with the previous constant speed train vibration test results,reflecting the particularity of the vibration caused by the train arriving at or leaving the station.4.The influence of passenger flow on the vibration source of metro trains is analyzed.The study on the influence of passenger flow on the vibration source is more practical.For this reason,the passenger volume distribution of the Beijing metro line has been investigated and counted.Considering the large commuting demand of the Beijing Metro Line 4,the passenger volume distribution between Xidan and Xuanwumen section was analyzed in detail.It was found that the peak of passenger volume occurred at 6:30-9:30 AM and 17:00-20:30 PM on Friday,and the maximum load factor during peak hours was up to 130%,even if the departure interval is shortened,a better mitigation effect is not achieved.The influence of passenger volume distribution on the vibration source characteristics of metro trains arriving at or leaving the station is as follows:the peak value of the vibration source occurs during the morning and evening peak hours of passengers on Friday,lasting nearly two hours;along the moving direction,the vibration acceleration amplitude on ground surface induced by the leaving station is more sensitive to changes in passenger capacity.Through the theory and test analysis above,the basic laws of vibration source characteristics of metro trains arriving at or leaving the station are preliminarily obtained,which provide some reference for related building renovation,environmental protection and metro reduction and vibration isolation design.