Numerical modelling of track-ground response induced by train passage

Abstract

The global railway network is undergoing rapid expansion, with train vehicles becoming faster. Increases to operational train speed mean that it is more likely vehicles will induce larger dynamic effects within the supporting track and soil structure. At the same time, it is challenging to determine the type and depth of ground remediation required to reduce the track deflections. The present dissertation addresses the subject of vibrations induced by the passage of high-speed trains. The main aim of this work is to develop numerical tools that allow analysing track behaviour efficiently, investigating material non-linearity effect on the track dynamics, and also assessing the soil remediation strategies. Firstly, A semi-analytical model is proposed and designed for the dynamic analysis of track-ground vibrations induced by high speed rails. The model uses analytical expressions for the railroad track, coupled to a thin-layer element formulation for the ground. 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. Moreover, it is used to investigate the effect of soil replacement/improvement below railway lines due to its low computational costs. Secondly, new insights are given to non-linear subgrade behaviour on high speed railway track dynamics. Built upon the proposed semi-analytical model, material non-linearity is accounted for using a ‘linear equivalent’ approach which iteratively updates the soil material properties. The model is validated using published datasets and in-situ field data. Four case studies are used to investigate the non-linear behaviour, each with contrasting subgrade characteristics. It is found that the critical velocity can shift to as low as 80% of the linear case, while rail deflections are up to 30% higher, depending on the material properties. Finally, a novel 2.5D FEM-BEM-TLM model is developed to include material non-linearity for both track structure and soil. The track structure is represented by a finite element model and the soil responses are obtained from boundary element model and thin-layer model. Material non-linearity is included using the proposed ’linear equivalent’ approach. The model is validated against the commercial FE software ABAQUS and numerical results from published literature. Two case studies are conducted to shed light upon the full material non-linearity effect on the dynamic track-ground responses from the train passage, revealing the necessity of its use, especially when high strains occur.