孔隙水压力对高铁路基动力响应的影响

Influence of Pore Water Pressure on Dynamic Response of High-speed Rail Subgrade

采用2.5维有限元方法分析孔隙水压力对饱和路基地面振动的影响。根据Biot理论建立饱和多孔介质控制方程,采用双重Fourier变换将控制方程转换为频率-波数域表达式。采用2.5维有限元方法建立饱和路基模型,列车荷载在频率-波数域表示,轨道和路堤采用欧拉梁模拟,采用黏滞阻尼吸波边界减小有限元边界反射。分析列车速度、路基孔隙率和渗透系数对地面振动和孔隙水压力的影响。结果表明:车速较低时,由于饱和路基受孔隙水压力的影响,地面竖向振幅小于弹性地基;车速较高时,孔隙水压力急剧增加,对地面振动影响较大。列车运行速度较高时,饱和地基的孔隙率和渗透系数对孔隙水压力有较大影响。

Ground vibration in a saturated subgrade caused by a high-speed train differs from that by a low-speed train.However,few studies focus on the influence of pore water pressure on ground vibration even though the key reason for the difference in ground vibration between saturated and elastic subgrades is a function of pore water pressure.Therefore,it is necessary to analyze the characteristics of the alteration of pore water pressure under various train speeds and to discuss the influence of pore water pressure on ground vibration.The 2.5-D finite element method（FEM）is used to analyze the influence of pore water pressure on the ground vibration of saturated subgrade.On the basis of the Biot theory,the governing equations of saturated porous media are established and transformed into frequency-wave number domains by double Fourier transform.The track and embankment are modeled by Euler beam.The saturated subgrade is modeled by 2.5-D FEM,and the train loading in the model is also transformed into frequency-wave number domains.The viscous damping absorbing boundary is used to reduce the influence of the finite element（FE）boundary.The 2.5-D FE model is validated by field vibration test results of the Sweden X2000high-speed train.The results of the 2.5-D FE model match the field test results both in vibration interval and displacement amplitude.Therefore,this 2.5-D FE subgrade model is reliable for studying ground vibration in saturated sub-grade.The paper discusses the influence of train speed,porosity,and coefficient of permeability of the saturated subgrade on ground vibration.The results show that when the train speed is low,the vertical vibration amplitude of the saturated ground is smaller than that of the elastic ground due to the influence of pore water pressure.However,when the train speed is high,the pore water pressure rises sharply and notably affects the ground vibration.The train loadings share the soil skeleton and the excess pore water pressure,which leads to the decrease of stress in the soil caused by the train loadings and the decreasing in vibration amplitude.When the train speed is larger than the Rayleigh wave velocity of the soil,or close to the shear wave velocity,there are several critical velocities.When the train speed is larger than the first velocity,a second velocity occurs that may lead to the increase in ground vibration amplitude.Thus,when the train speed is252km/h,the vibration amplitude increases and approaches that of the elastic model.The increase in train speed increases the high-frequency vibration in the subgrade,which leads to a sharp rise in excess pore water pressure owing to relatively slow pore water pressure dissipation.When as the train speed is very high,the changing of stress in the subgrade is assumed mainly by the excess pore water pressure,and the soil skeleton is less affected.As a result,the excess pore water pressure causes a small alteration of the amplitude of ground vibration when the train speed changes to high speed.The influence of porosity and permeability coefficient of the saturated subgrade on the pore water pressure is notable when the train speed is high.The results show that when the train speed is high,the pore water pressure of the saturated subgrade increases as the porosity decreases.As the permeability of the saturated subgrade increases,the pore water pressure within a 0.5mdepth increases,and deeper pore water pressure decreases.Therefore,to control ground vibration in the saturated subgrade,compact material with high permeability is suggested for subgrade material.