| With the continuous growth of China’s economy and the further development of urbanization,the contradiction between urban rail transit construction and the shortage of land resources has become increasingly prominent.Using the upper space of metro depot for property development has become the trend of subway system construction in major cities.However,the operation of trains in the metro depot is easy to cause the structural vibration and secondary radiated noise within the over-track building,which thereby reduces its comfort.The existing research on the influence of the comfort of properties above metro depots is mainly carried out for a single over-track building.A clear and unified understanding has not been formed on the dynamic characteristics and interactions of vibration source,propagation path and the vibrating body.There is a lack of sufficient research on the dynamic interaction mechanism of soil,pile foundation and superstructure under the environmental vibration input caused by train operations in the metro depot.Research on the influence of transfer structures on the train-induced vibration propagation law is also inadequate.Improper prediction and evaluation of train-induced vibration can easily lead to poor design of vibration control measures for building structures,and can even cause undesirable environmental vibration and noise pollution.To fully understand the propagation law of train-induced vibration in the metro depot with over-track buildings,further improve the prediction method of train-induced vibration in the depot and scientifically guide the design of vibration reduction and isolation technical measures,based on typical metro depots in the Pearl River Delta,this paper systematically studies the prediction method of train-induced vibration of over-track buildings considering the dynamic coupling of soil-pile-superstructure through field test and theoretical analysis.The main research work and achievements of this paper are as follows:(1)Through field study,it is found that under the train-induced environmental vibration input in the metro depot,the soil to structure vibration transfer function generally decreases with the increase of frequency,but it does not decrease monotonically.The transfer function is closely related to the dynamic characteristics of soil,pile foundation and superstructure.Within the frequency range of 8～80 Hz,the coupling loss at shear wall base with pile group foundation is-20～-5 d B while at platform column base with single pile is-12～+2 d B,where both locations15 m away from the track centerline.The larger the stiffness of the pile foundation and the volume of the superstructure,the greater the energy loss when train-induced vibration transmitting from the soil to the superstructure;Due to its strong bending stiffness,the transfer structure is conducive to blocking the vertical propagation of train-induced vibration to a certain extent;When the train in the throat area runs on different tracks in the horizontal projection area of the superstructure,the specific position of the operating line has little effect on the vibration within the over-track buildings because the train-induced vibration propagates to the transfer floor and over-track building through different platform columns and has multiple propagation paths;The vertical propagation law of train-induced vibration along the column of the overtrack frame building is related to the impedance of the floor system.The greater the impedance of the floor system,the more obvious the attenuation of train-induced vibration along with the increase of floors.(2)Based on the assumption of excitation statistical independence and the thin-layer stiffness method in frequency-wavenumber domain,a prediction model of train-induced free field soil vibration in the metro depot is constructed,which can effectively predict the soil vibration response to different marshalling trains,and provide necessary vibration input for the prediction model of soil-pile-superstructure dynamic interaction.The results show that under the same rectangular harmonic stress on the surface,the medium to high frequency components of vibration at soil surface is larger when the shear wave velocity of the topsoil is smaller;In a certain frequency range,when the buried depth of bedrock is greater than the maximum shear wavelength,the influence of bedrock characteristics on surface vibration response can be ignored;When the buried depth of bedrock is less than the shortest shear wavelength,the influence of bedrock on the surface vibration response is mainly reflected in increasing the overall stiffness of soil and reducing the surface vibration response.(3)The prediction model of soil-pile dynamic interaction is established,and the effects of pile-soil stiffness ratio,pile length,pile diameter and rock socketed length on the vibration propagation law from soil to pile foundation are studied: the greater the stiffness difference between pile foundation and soil,the more significant the kinematic effect of pile foundation under environmental vibration;Under the excitation of surface load,when the pile length exceeds the influence depth of Rayleigh wave,the continuous increase of pile length is not helpful to reduce the vibration response at free pile head;Increasing the pile diameter can not reduce the vibration response of free pile head under environmental vibration in the full frequency band.(4)Based on the impedance theory,the calculation formula of pile-superstructure dynamic characteristics coupling is proposed,the analytical prediction model of pile-superstructure dynamic interaction is constructed,and the inertia effect in soil-pile-superstructure dynamic interaction is studied: the superstructure will inhibit the vertical vibration of free pile head,and the significance of the inhibition depends on the relative impedance between the pile head of the lower foundation system and the base of the superstructure system,When the latter is greater than the former,the dynamic characteristics of the superstructure have an obvious inhibitory effect on the vertical vibration of the free pile head,and the vibration amplitude of the pile head will be greatly reduced.(5)Based on the impedance of column,beam and plate elements in frequency domain,a prediction model of train-induced vibration at column bases within over-track framed buildings with transfer structures is established.The vertical propagation of train-induced vibration in the form of axial wave in the platform column and the horizontal propagation in the form of bending wave in the transfer beam are studied: the contribution of platform column to train-induced vibration of over-track building is mainly related to the vibration propagation distance between them and the axial impedance of platform column.The farther the distance is and the smaller the axial impedance is,the smaller the energy contribution is.The input contribution of platform column outside the plane projection area of the over-track building can be ignored in the prediction and analysis.(6)Based on the wave theory,the expression of vertical motion impedance at the beam end considering the composite action and the coupling effect of bending vibration between beam and slab is derived.The prediction method of average vibration response of floor slab of over-track frame building in metro depot is proposed.The train-induced vibration propagation law within the over-track framed building is studied: when the train-induced vibration propagates upward along the structural column in the form of axial wave,part of the vibrational energy is dissipated through the floor system.Increasing the impedance of the floor system is helpful to reduce the propagation of train-induced vibration to the upper floors.The prediction model method has the advantages of short calculation time,high prediction accuracy and small modeling workload,which is convenient for engineering practical application.It is suitable for conducting vibration prediction analysis before the structural design and construction of overtrack building in metro depots,and for evaluating the influence of train-induced vibration on human comfort.It provides scientific guidance for the planning and layout of the over-track properties in metro depots and the design of vibration reduction and isolation technical measures. |
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