Study On Vehicle-induced Vibration Response Of Shield Tunnel In Water-rich And Soft-weak Strata

In the process of subway construction,it is inevitable to pass through the soft stratum which is rich in ground water.Under the action of train vibration load,such stratum has potential risks such as decreased bearing capacity and vibration collapse,which may affect the safe operation of the train.Based on the domestic and foreign research status,this paper further studies dynamic response characteristics of shield tunnel and surrounding stratum under train vibration load in water-rich and soft stratum by means of model test and numerical simulation.The influence law of groundwater on the dynamic response of the tunnel structure and stratum is analyzed emphatically,and the development law of pore water pressure of soil around the tunnel under the action of train vibration load is ascertained.The specific work carried out is as follows:（1）Based on the developed fluid-structure coupled dynamic test device,indoor model tests were carried out to test the dynamic response of tunnel structure and stratum in water-rich and soft stratum under single point excitation load.Firstly,the coherence coefficient is introduced to analyze the reliability of model test data.The analysis results show that the reliability of the test data is low in the frequency range of 0～40Hz.In the frequency range of40-250Hz,the test data is less affected by the environmental interference.（2）The finite difference software FLAC^3D was used to carry out the numerical simulation research,and the calculated results were in good agreement with the experimental results,which verified the reliability of the two research methods.The dynamic response characteristics of tunnel structure and stratum in low frequency band（less than 40Hz）were further studied to obtain the toroidal stress response law of tunnel lining,and the temporal development law and spatial distribution law of excess pore water pressure of soil around the tunnel under single point train vibration load were deeply explored.The results show that the dynamic response of the tunnel structure and stratum is obviously attenuated under the influence of groundwater,especially in the high frequency band（180Hz～250Hz）.The circumferential stress response of the tunnel structure at the section under excitation load is obviously larger than that at other locations,with the phenomenon of stress concentration（circumferential 180°）.Under the influence of groundwater,there will be an obvious amplification effect.Under the action of train vibration load,the excess pore water pressure of the surrounding soil oscillates and rises,and mainly distributes in the area around the tunnel,especially in the outer part below the arch foot of the tunnel.（3）On the basis of discovering the dynamic response of tunnel structure and stratum under single point vibration load,further considering the train running effect,the dynamic response of tunnel structure and stratum in water-rich and soft stratum under moving train vibration load is calculated.The parametric sensitivity of the tunnel structure and the stratum to the vehicle-induced vibration response in the water-rich soft stratum is analyzed from the perspectives of pore water pressure and acceleration.The results show that the acceleration response of the tunnel structure and the ground layer attenuates to a certain extent under the influence of the groundwater,and the attenuations are most obvious in the two sides of the arch foot and the far surface respectively.The circumferential stress of the lining structure is the most sensitive to train vibration,and the amplitude of circumferential stress response increases by 66.34%under the action of groundwater.The acceleration response of tunnel structure and stratum decreases with the decrease of train speed,and the overall difference of peak acceleration is more than 90%.The acceleration response of tunnel structure and stratum is affected to some extent by the way of segment assembly and the permeability of soil,but the average difference of peak acceleration is less than 20%.The excess pore water pressure of the surrounding soil is most obviously affected by the speed of the vehicle,followed by the permeability of the soil,and the least affected by the way of segment assembly.