列车荷载作用下冻土路基中的动应力计算研究

冻土路基在列车荷载作用下的动力响应是一个复杂的热、力相互作用过程，又是一个急需解决的实际工程难题. 应用冻土物理学、冻土力学、传热学等基本理论建立冻土路基的动力分析模型，以青藏铁路某普通路基典型断面为例，对冻土路基在列车荷载作用下的动力响应进行了数值模拟，并系统的分析了路基内动应力、位移、加速度等动力响应特点. 结果表明：普通路基修筑后，在路基及其下部地基中将会产生大片力学性质不稳定的高温冻土层；在列车荷载作用下，路基内土体产生竖向加速度，随着深度增加，加速度波动范围减小，路基顶面中心点加速度波动范围比路基底面中心点大一个量级. 路基竖向位移由道砟中心向内部呈圆弧状逐渐减小，整个分布关于路基中线对称；在不同季节的路基上施加列车荷载时，路基顶面的动应力差异不大，但路基底面的动应力差异达7.5 kPa. 不同季节的路基内动应力随深度的衰减曲线不同，路基表面以下2 m和大于15 m的深度范围内，差异较小；2~15 m的范围内，差异较大.

Research on the Calculation of Dynamic Stress of Embankment in Permafrost Regions Under Train Load

Dynamic response of embankment to train load in permafrost regions is a complicated interaction course between heat and force, and is also an engineering problem which is badly in need of solving. Using fundamental principles of physics of frozen soil, mechanics of frozen soil, heat transfer, a dynamic analysis model for embankment in permafrost regions is developed. Then, taking a typical section of the Qinghai-Tibet Railway as an example, dynamic response of embankment to train load is simulated, and dynamic stress, acceleration and displacement in the embankment are analyzed in detail. The following conclusions are drawn: (1) according to the calculation result of temperature field, a block of high temperature frozen soil takes place inside the embankment and its foundation, where mechanical property of the frozen soil becomes unstable after construction of embankment; (2) vertical acceleration takes place inside the embankment due to train load, and fluctuation range of the acceleration decreases with depth; fluctuation range of the center point of the top embankment surface is larger than that of the center point of the embankment bottom with an order of magnitude; (3)under train load, embankment displacement gradually decreases from ballast center to inside with an arc shape, and the displacement distribution has a symmetry form to the embankment midline; (4)seasonal difference of dynamic stresses is small on the embankment surface, but it is 7.5 kPa on the embankment bottom; (5) the attenuation curve of dynamic stress is different among different seasons, and the differences of the curves are small at the depth less than 2 m or more than 15 m below the embankment surface, but they are large in the depth range from 2 to 15 m below the embankment surface.