Train-induced Vibration Transmission And Mitigation In Metro Depot And Over-track Buildings

Transit-oriented development,such as metro depot and over-track building complexes,has expanded rapidly in China.Over-track building construction has the advantage of comprehensive utilization of land resources,ease of commuting to work,and provide funds for subway construction.But the high frequency of subway operations into and out of the depots can generate excessive vibrations that transmit into the over track buildings through foundation and platform,and adversely affect the living quality of the building occupants.To decrease and eliminate the vibration impacts becomes the key factor for the development of metro depot and over-track buildings.This study focuses on the influence of subway train-induced vibration on the ground and inside adjacent building and over-track buildings in typical metro depots in the Pearl River Delta Region in order to characterize the vibration transmission in the metro depot and over-track buildings,and develop efficient and cost-effective methods to mitigate the vibration for human comfort and propose an efficient predicted method for building vibration.The main research contents and results are shown below,(1)Field measurements of vibration during subway operations were conducted in typical metro depots and over-track buildings in the Pearl River Delta Region to study vibration transmission on the ground,near the building and in the over-track buildings in the throat area and near the testing line.The results showed that train-induced ground vibration and platform vibration reduced with the distance away from the track.The vertical vibrations were significantly greater than the horizontal vibrations in the buildings,and the vibration decreased with the height of the low-rise building.For the high-rise over-track buildings,the vibration increased slightly on the lower floors,and then decreased on the middle floors and finally amplified on the top floor.(2)The train-track dynamic coupling model was developed to analyses wheel-rail contact force changed with time history by using Newmark implicit integration algorithm.The coupling of train model and track model was used wheel-rail irregularity as the excitation based on the force equilibrium and displacement coordination of wheels and rails.The reasonability and accuracy of the model was verified by the comparison of the calculated data with reference case and measured data.(3)The track-soil-adjacent building finite element model was built using moving load as exciation to characterize the vibration transmission on the ground and in the adjacent building,and the reasonability and accuracy of the model was verified by comparing the calculated data with measured data.In addition,the impact of different foundation soil properties on vibration transmission was studied.The results showed that the shear wave velocity of soil has the significant impact on ground vibration.The building vibration decreased with the increasing shear wave velocity of soil.The peak value frequency of building vibration was influence by soil and structure interaction,and the frequency increased with the increasing shear wave velocity.(4)The track-soil-over-track building finite element model was built to study the vibration mitigation by wave barriers.The optimum dimensions of open trench were discussed and different materials in-fill trenchs were analyzed.The novel composite type of wave barriers,which has the advantage of stiff materials or flexible materials in-fill trench and open trench,was proposed to reduced vibration transmission.In addition,the effectiveness of using concrete wall and foundation improvement to reduced vibration transmission was studied.The results showed that the effectiveness of stiff material in-fill trench was better than flexible materials in-fill trench.However,open trench has the best efficiency for reducing vibration transmission at the major frequency band,and the efficiency of concrete wall was worse.The mitigation efficiency of using flexible material composite wave barrier was better than using flexible material in-fill trench,but the mitigation efficiency of using stiff material composite wave barrier was worse than using stiff material in-fill trench.Foundation improvement has the advantage to incresing the impedance of soil to reduce the vibration transmission in the building.(5)In order to predict train-induced vibration levels in the over-track buildings before construction,one-dimensional(1D)and two-dimensional(2D)frequency-dependent impedance models were presented based on rod,beam and plate impedance expressions.The model takes into account the propagation of axial waves and bending waves through columns or load-bearing walls,respectively.By comparing the power transmitted for an incident wave with the same velocity in both the vertical and horizontal directions,the significance of wave incidence and wave type in the vertical components can be found based on 2D impedance model.The measured train-induced vibrations in a 14-story building and a 25-story building was used to validate the proposed impedance model.The results showed that the models were in good qualitative agreement with measured floor response.1D impedance model and 2D impedance model both yield comparable velocity levels at each frequency in the 1/3 octave spectrum due to both models capture the important path of axial wave transmission for vibration transmission up through the columns/walls.(6)A sensitivity analysis of the 2D impedance model was performed by considering the number of stories,cross-section area of vertical components,floor thicknesses,density and elastic modulus of vertical components` and floors` material,and lightweight fill in floors.The results showed that the high-rise building`s vibration was lower that low-rise building` vibration.Increasing floor thickness was the fastest way to obtain high floor impedance has the advantage of blocking/reducing the vertical vibration transmission to the upper floors.Lightweight concretes used for lightweight fill solutions in building`s floors can decrease building`s weight that added by increasing floor thickness to increase impedance and decrease the risk of earthquake.The thesis provides the new impedance model was developed to predict train-induced vibration levels in the over-track buildings.The findings can provide useful insight for designing vibration mitigation systems in new metro depots with over-track buildings.