高速列车荷载作用下饱和软土地基动力响应研究

Dynamic responses of saturated soft soil foundation under high speed train

基于Biot多孔介质理论,建立了车辆-轨道-饱和地基耦合系统的2.5维有限元分析模型,研究了高速列车荷载作用下饱和软土地基动力响应的发展规律。研究结果表明:当列车速度小于系统临界速度时,列车荷载在饱和软土中引起的最大超静孔压值由列车运行速度c和饱和土渗透系数k_(D)的比值c/k_(D)决定。对于本模型中的饱和软土,当c/k_(D)≤3×10^(4)时,饱和土中几乎不会产生超静孔压,此时饱和地基可以被当作弹性地基处理。饱和软土地基中的超静孔压随c/k_(D)单调增长,并且存在一个临界c/k_(D)值,对应超静孔压能够达到的最大值;超过临界c/k_(D)值后,超静孔压不再随c/k_(D)的变化而变化。饱和软土地基中,有效应力的响应强度和作用范围主要由列车速度和饱和土渗透系数共同控制;但位移响应与渗透系数无关,主要受列车速度控制。特别地,当列车速度达到或超过系统临界速度时,饱和软土地基中会出现显著的马赫效应。

Based on the Biot theory of porous media, this paper proposes a coupled vehicle-track-saturated foundation model to study the dynamic responses of saturated soft soil foundation under high speed train via two-and-half dimensional finite element method(2.5 D FEM). It is found that the ratio of train speed c and soil Darcy permeability k_(D)(c/k_(D)) determines the extent to which maximum excess pore pressures build up in saturated soft soil under the train load when the load speed is lower than the critical speed.For a saturated soil of a particular stiffness, if c/k_(D) is less than or equal to 3×10^(4), the soil can be viewed as highly permeable in relation to the load velocity and almost no excess pore pressure is developed, the saturated soil can be modeled using single-phase medium. There is a critical value of c/k_(D) for the development of excess pore pressure, when c/k_(D) is smaller than the critical value, the maximum excess pore pressure increases with increasing c/k_(D). Above the critical value of c/k_(D), the maximum excess pore pressure remain independent of c/k_(D). The amplitude and affect scope of effective stress are mainly controlled by train speed and soil permeability for saturated soft soil foundation. The response of displacement is mainly controlled by the train speed.Significant Mach effects have been induced in the saturated soil foundation by the moving train, when the train speed reaches or exceeds the critical velocity of the track-foundation system.