列车加减速引起轨道结构和饱和地基振动

为了研究列车加减速引起的饱和地基振动问题,基于两相介质Biot动力控制方程的简化u-p格式,开发二维饱和土体单元. 通过引入饱和土体黏弹性人工边界,求解移动点荷载作用下的二维饱和地基动力响应,并与半解析解进行对比验证,说明饱和土体单元的正确性和黏弹性人工边界的适用性. 结合E-B梁单元、弹簧-黏壶单元和集中质量单元对轨枕、道砟离散支承的轨道结构及饱和地基进行二维有限单元离散. 将列车荷载简化为平面内的移动轴荷载,通过与列车匀速时对比研究列车加速和减速时饱和地基的孔压、位移响应及离散轨枕、道砟的加速度响应. 结果表明列车减速将增大轨枕、道砟的水平及竖向加速度峰值；列车加速和减速在饱和地基中引起方向相反的土体水平向位移,且减速时土体水平位移峰值更大；列车加速和减速均增大土体竖向位移峰值.

Study on vibrations of rail structure and saturated soil induced by train acceleration and deceleration

Based on the simplified u-p formulation of Biot's theory, a 2D saturated-soil element was developed and used to discretize a saturated ground under plain-strain condition. At boundaries of the saturated ground model, artificial boundary conditions were applied to simulate the infinity of the ground. The rail, rail-pads, sleepers and ballasts of a 2D track were modeled by E-B beam elements, spring-damper elements and lumped mass elements, respectively. The train loads were simplified into a series of moving axle loads in plain. By comparing to the case of a train under uniform motion, the effects of train acceleration and deceleration were investigated with respect to the track accelerations, the displacements and excess pore water pressures of the saturated ground. It is found that peak values of the horizontal and vertical accelerations of the sleeper and ballast are increased by train deceleration; train acceleration and deceleration cause horizontal ground displacements in opposite directions; the peak value of horizontal ground displacements caused by train deceleration is larger than that induced by train acceleration; both of train acceleration and deceleration slightly increase peak values of the vertical ground displacements.