The stiffening of soft soils on railway lines
The stiffening of soft soils on railway lines
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DOI：
10.1016/j.trgeo.2018.09.004
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发表时间：
2018-12-01
影响因子：
5.3
通讯作者：
Costa, P. Alves
中科院分区：
文献类型：
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作者：
Dong, K.;Connolly, D. P.;Costa, P. Alves
当支承土壤较软和/或列车速度大于轨道-土壤系统中的波传播速度（即临界速度）的约50%时，铁路轨道会经历高架轨道偏转。这样的振动是不希望的，因此土壤置换或天然土壤的土壤改良（或替代性地微型桩或石灰水泥处理）通常用于在线路施工之前增加轨道地面刚度。虽然在潜在的新铁路线上可以很容易地识别现有的软路基区域，但确定所需的地面修复类型和深度具有挑战性。因此，主要的成本节约可以通过优化地面更换/改善strategy.This本文提出了一个数值铁路模型，设计用于动态分析的轨道地面振动引起的高速铁路线。该模型使用薄层有限元公式模拟地面，该公式能够计算列车车辆通过期间土壤内的3D应力和应变。铁路轨道建模使用多层配方，允许波在纵向方向上传播，并耦合在频率波数域中的土壤模型。该模型是使用实验铁路现场数据，公布的数值数据和商业有限元软件包的组合进行验证。它被证明是准确地预测轨道和地面行为的列车速度范围。铁路仿真模型是计算效率高，能够快速评估动态，多层土壤中存在的道碴和板式轨道结构的反应。因此，它非常适合于分析不同土壤置换策略对动态轨道行为的影响，这在接近临界速度时尤为重要。为了证明这一点，三个土壤路堤的例子是用来比较不同的组合的刚度改善（刚度大小和补救深度高达5米）的轨道行为的影响。据发现，必须根据轨道类型和现有的路基分层配置仔细选择改进策略。在某些情况下，土壤改良的效果可以忽略不计，甚至可能导致高架轨道振动，这可能会增加长期沉降。然而，如果进行详细的分析，可能会带来很大的好处，就施工成本而言，可以最大限度地减少土壤改良深度。
Railway tracks experience elevated rail deflections when the supporting soil is soft and/or the train speed is greater than approximately 50% of the wave propagation velocity in the track-soil system (i.e. the critical velocity). Such vibrations are undesirable, so soil replacement or soil improvement of the natural soil (or alternatively mini-piles or lime-cement treatment) is often used to increase track-ground stiffness prior to line construction. Although areas of existing soft subgrade might be easily identified on a potential new rail route, it is challenging to determine the type and depth of ground remediation required. Therefore, major cost savings can be made by optimising ground replacement/improvement strategies.This paper presents a numerical railway model, designed for the dynamic analysis of track-ground vibrations induced by high speed rail lines. The model simulates the ground using a thin-layer finite element formulation capable of calculating 3D stresses and strains within the soil during train vehicle passage. The railroad track is modelled using a multi-layered formulation which permits wave propagation in the longitudinal direction, and is coupled with the soil model in the frequency-wavenumber domain. The model is validated using a combination of experimental railway field data, published numerical data and a commercial finite element package. It is shown to predict track and ground behaviour accurately for a range of train speeds.The railway simulation model is computationally efficient and able to quickly assess dynamic, multi-layered soil response in the presence of ballast and slab track structures. Therefore it is well-suited to analysing the effect of different soil replacement strategies on dynamic track behaviour, which is particularly important when close to critical speed. To show this, three soil-embankment examples are used to compare the effect of different combinations of stiffness improvement (stiffness magnitude and remediation depths up to 5 m) on track behaviour. It is found that improvement strategies must be carefully chosen depending upon the track type and existing subgrade layering configuration. Under certain circumstances, soil improvement can have a negligible effect, or possibly even result in elevated track vibration, which may increase long-term settlement. However, large benefits are possible, and if detailed analysis is performed, it is possible to minimise soil improvement depth with respect to construction cost.