The substantial increase in excess pore pressure and plastic strain in subgrade soil due to faster and heavier trains is a major cause of track instability. Stresses that occur in track substructure during the passage of trains have not often been captured accurately due to insufficient rigour in dynamic analysis. This paper presents a numerical investigation into the plastic/dynamic characteristics of a saturated porous medium (capping and subgrade) subjected to moving axle loads. In this study, a detailed numerical analysis is described, whereby a coupled fluid-dynamic framework is developed for the saturated porous medium in conjunction with a generalized plasticity model, in order to examine the cyclic loading response of a soft subgrade soil. The constitutive model is calibrated by undrained cyclic triaxial testing carried out on a soft foundation soil retrieved from a coastal railroad site having a historical record of mud pumping. Kelvin elements are attached to the transmitting boundary to absorb wave energy and to prevent any back-propagation of waves into the saturated subgrade domain. This approach is then validated against a semi-analytical solution and wayside measurements. The results show that the stress path corresponding to the applied moving load exhibits a series of heart-shaped envelopes along which the deviator stress and mean effective stress gradually decrease with the successive loading cycles. The build-up of pore water pressure and the associated soil deformation (e.g. accumulated settlement) are exacerbated when the train speed approaches a critical velocity of the saturated subgrade. A relationship between the train speed, track settlement and drainage capacity of a sub-ballast (capping) layer is also established. As a practical guide, the influence of permeability of the capping layer is highlighted in relation to controlling track settlement for a given operational train speed.

由于列车速度更快和重量更大，导致路基土壤中的过大孔隙压力和塑性应变大量增加，这是轨道不稳定的主要原因。由于动态分析中的严谨性不足，通常无法准确地捕获列车通过时在轨道下部结构中产生的应力。本文提供了数值模拟，研究了轴心移动时饱和多孔介质（盖和路基）的塑性/动力特性。在这项研究中，描述了详细的数值分析，从而结合广义塑性模型为饱和多孔介质建立了耦合的流体动力框架，以研究软基土的循环荷载响应。本构模型通过不排水循环三轴试验进行校准，该试验在从有泥浆泵送历史记录的沿海铁路站点取回的软土地基上进行。开尔文单元连接到传输边界，以吸收波能并防止波向后传播到饱和路基区域。然后针对半分析解决方案和路边测量对这种方法进行验证。结果表明，与施加的移动载荷相对应的应力路径表现出一系列心形包络，沿着这些包络，随着连续的载荷循环，偏应力和平均有效应力逐渐减小。孔隙水压力的增加和相关的土壤变形（例如 当列车速度接近饱和路基的临界速度时，累积沉降会加剧。还建立了列车速度，轨道沉降和子道ball（封顶）层的排水能力之间的关系。作为实用指南，在给定的运行列车速度下，与控制轨道沉降有关，强调了覆盖层的磁导率的影响。