Numerical prediction of low-frequency ground vibrations induced by high-speed trains at Ledsgaard, Sweden

The ground vibrations induced by a passenger train at the test site of Ledsgaard, Sweden, have been analysed and numerically simulated through a spectral element discretization of the soil. To calculate the spatial distribution of loading due to train passage, the train is decoupled from the track, and a suitable series of static forces is applied. The track and the embankment are modeled as a beam on elastic foundation, using analytical solutions for loads moving at constant velocity. The results of both 2D and 3D modelling assumptions are thoroughly discussed, in terms of prediction of track motion and of attenuation of peak ground velocity with distance.     

A semi-analytical approach for analyzing ground vibrations caused by trains moving over elevated bridges

A semi-analytic approach is presented for the three-dimensional analysis of ground vibrations induced by trains moving over elevated bridges. The train is modeled as two sets of moving loads, with one for the front wheels and the other for the rear ones, the elevated bridge as a series of elastically supported beams, and the ground as a viscoelastic half space. Three key elements are considered in the solution: (1) the analytic solution for the vibration of an elastically supported beam under a series of moving loads, (2) the impedance of the foundation–soil system, and (3) Green's function for an elastic half space under a harmonic point load. Such an approach allows us to consider the structural dynamics of the elevated bridge, the foundation–soil interaction, and the wave propagation characteristics in the half space. From the numerical examples studied, the proposed approach was demonstrated to be accurate and efficient. The framework of analysis described herein can be generalized to solve problems with complex foundations and layered soils.     

Field testing and analysis of high speed rail vibrations

This paper outlines an experimental analysis of ground-borne vibration levels generated by high speed rail lines on various earthwork profiles (at-grade, embankment, cutting and overpass). It also serves to provide access to a dataset of experimental measurements, freely available for download by other researchers working in the area of railway vibration (e.g. for further investigation and/or the validation of vibration prediction models).First, the work outlines experimental investigations undertaken on the Belgian high speed rail network to investigate the vibration propagation characteristics of three different embankment conditions. The sites consist of a 5.5 m high embankment, an at-grade section and a 7.2 m deep cutting. The soil material properties of each site are determined using a ‘Multichannel Analysis of Surface Waves’ technique and verified using refraction analysis. It is shown that all sites have relatively similar material properties thus enabling a generalised comparison.Vibration levels are measured in three directions, up to 100 m from the track due to three different train types (Eurostar, TGV and Thalys) and then analysed statistically. It is found that contrary to commonly accepted theory, vertical vibrations are not always the most dominant, and that horizontal vibrations should also be considered, particularly at larger offsets. It is also found that the embankment earthworks profile produced the lowest vibration levels and the cutting produced the highest. Furthermore, a low (positive) correlation between train speed and vibration levels was found. A selection of the results can be downloaded from www.davidpconnolly.com.     

A 3D BEM-FEM methodology for simulation of high speed train induced vibrations

This work presents an efficient methodology for the analysis of vibrations in a railroad track system, induced by the passage of conventional and high-speed trains. To this end the Boundary Element Method is used to model the soil-tie system within the framework of impulse response techniques. Conventional Finite Element Methods along with Newmark's integration is used for the modeling of the rail system. The two methods are coupled at the tie-rail interface and the solution is obtained following a staggered, time marching scheme in an efficient manner. The methodology accounts for Soil-Structure Interaction and traveling wave effects. In addition, this work identifies the parameters that affect the efficient modeling of railroad track systems as they pertain to the proposed solution methodology.     

Behavior of ground vibrations induced by trains moving on embankments with rail roughness

This study investigates the behavior of ground vibrations induced by trains moving on embankments using theoretical formulations, finite element analyses, and field experiments. The train-induced vibrations are large at the dominant frequencies of nV/L_c, even though the rail is very rough, where n is a positive integer, V is the train speed, and L_c is the carriage interval. For subsonic train speeds, the train-induced ground vibration is extremely small when the rail is perfectly smooth, but with a minor rail irregularity, the train-induced ground vibration can be significantly increased. However, for supersonic train speeds, the ground vibrations with or without rail irregularities are not very different, and the vibration of the first dominant frequency having the longest wavelength is the most obvious wave.     

Experimental investigation of railway train-induced vibrations of surrounding ground and a nearby multi-story building

In this paper, a field experiment was carried out to study train-induced environmental vibrations. During the field experiment, velocity responses were measured at different locations of a six-story masonry structure near the Beijing-Guangzhou Railway and along a small road adjacent to the building. The results show that the velocity response levels of the environmental ground and the building floors increase with train speed, and attenuate with the distance to the railway track. Heavier freight trains indu...     

Assessment of railway vibrations using an efficient scoping model

Vibration assessments are required for new railroad lines to determine the effect of vibrations on local communities. Low accuracy assessments can significantly increase future project costs in the form of further detailed assessment or unexpected vibration abatement measures.This paper presents a new, high accuracy, initial assessment prediction tool for high speed lines. A key advantage of the new approach is that it is capable of including the effect of soil conditions in its calculation. This is novel because current scoping models ignore soil conditions, despite such characteristics being the most dominant factor in vibration propagation. The model also has zero run times thus allowing for the rapid assessment of vibration levels across rail networks.First, the development of the new tool is outlined. It is founded upon using a fully validated three dimensional finite element model to generate synthetic vibration records for a wide range of soil types. These records are analysed using a machine learning approach to map relationships between soil conditions, train speed and vibration levels. Its performance is tested through the prediction of two independent international vibration metrics on four European high speed lines and it is found to have high prediction accuracy.A key benefit from this increased prediction accuracy is that it potentially reduces the volume of detailed vibration analyses required for a new high speed train line. This avoids costly in-depth studies in the form of field experiments or large numerical models. Therefore the use of the new tool can result in cost savings.     

地铁列车曲线运行引起学校建筑物振动响应分析

地铁以其快捷、准时、运量大等优点,已成为重要的轨道交通形式,但由此引起的环境振动问题日益突出.针对杭州市地铁3号线曲线地段的某中学建设工程,利用有限元软件ABAQUS,对车辆-普通整体道床轨道系统的竖向耦合模型进行振动响应分析,得到考虑轨道高低不平顺影响的轨道振动源强.应用有限元软件MIDAS GTS/NX,建立双孔平...     

Numerical modelling of vibrations from a Thalys high speed train in the Groene Hart tunnel

This paper presents a numerical study of vibrations due to a Thalys high speed train in the Groene Hart tunnel, which is part of the high speed link South between Amsterdam and Antwerp and the world's largest bored tunnel.     

Scoping prediction of re-radiated ground-borne noise and vibration near high speed rail lines with variable soils

This paper outlines a vibration prediction tool, ScopeRail, capable of predicting in-door noise and vibration, within structures in close proximity to high speed railway lines. The tool is designed to rapidly predict vibration levels over large track distances, while using historical soil information to increase accuracy. Model results are compared to an alternative, commonly used, scoping model and it is found that ScopeRail offers higher accuracy predictions. This increased accuracy can potentially reduce the cost of vibration environmental impact assessments for new high speed rail lines.To develop the tool, a three-dimensional finite element model is first outlined capable of simulating vibration generation and propagation from high speed rail lines. A vast array of model permutations are computed to assess the effect of each input parameter on absolute ground vibration levels. These relations are analysed using a machine learning approach, resulting in a model that can instantly predict ground vibration levels in the presence of different train speeds and soil profiles. Then a collection of empirical factors are coupled with the model to allow for the prediction of structural vibration and in-door noise in buildings located near high speed lines. Additional factors are also used to enable the prediction of vibrations in the presence of abatement measures (e.g. ballast mats and floating slab tracks) and additional excitation mechanisms (e.g. wheelflats and switches/crossings).     

Mitigation of railway induced ground vibration by heavy masses next to the track

The effectiveness of heavy masses next to the track as a measure for the reduction of railway induced ground vibration is investigated by means of numerical simulations. It is assumed that the heavy masses are placed in a continuous row along the track forming a wall. Such a continuous wall could be built as a gabion wall and also used as a noise barrier. Since the performance of mitigation measures on the transmission path strongly depends on local ground conditions, a parametric study is performed for a range of possible designs in a set of different ground types. A two-and-a-half dimensional coupled finite element–boundary element methodology is used, assuming that the geometry of the problem is uniform in the direction along the track. It is found that the heavy masses start to be effective above the mass–spring resonance frequency which is determined by the dynamic stiffness of the soil and the mass of the wall. At frequencies above this resonance frequency, masses at the soil׳s surface hinder the propagation of surface waves. It is therefore beneficial to make the footprint of the masses as large and stiff as possible. For homogeneous soil conditions, the effectiveness is nearly independent of the distance behind the wall. In the case of a layered soil with a soft top layer, the vibration reduction strongly decreases with increasing distance from the wall.     

地铁诱发地面运动的衰减规律的研究分析

以地铁车站间的隧道为研究对象，在研究和分析有关资料的基础上，用快速拉格朗日有限差分法软件FLAC建立了二维数值分析模型，并以列车振动加速度时程作为模型输入，进行了隧道衬砌－地层的整体动力学分析，分析了列车运行产生的振动在地面的衰减规律，得到了一些结论，可为地面建筑的防振减振控制提供参考。     

高速铁路桩板结构对瑞利波的被动隔震试验研究

为研究高速铁路桩板结构被动隔震效果,以减震率作为隔震性能评价指标。通过模型试验分析不同几何参数的桩板结构隔震性能,并绘制减震率等值线图以描述其隔震区域。基于试验得到以下结论：桩板结构可以有效阻隔瑞利波,增加桩长、桩径和承载板厚度,并减小埋深与桩间距,可以提高隔震性能并增大有效隔震面积。减震率增长幅度随桩长、桩径和承载板厚度增大而减小,故桩径和桩间距参数宜控制在0.33至0.67之间,桩长参数宜控制在0.40至0.80之间,且应尽可能减小埋深。当砼使用方量相同时,隔震效果从强到弱依次为：桩长、承载板厚度和桩径。     

Seismic ground motion amplification pattern induced by a subway tunnel: Shaking table testing and numerical simulation

A series of 1 g shaking table tests, followed by the numerical simulations, is performed to investigate the effect of a circular subway tunnel on the ground motion amplification pattern. Effects of various parameters, including shear wave velocity of soil, frequency content of input motion, flexibility ratio and tunnel depth on the amplification pattern is investigated. Experimental study revealed that the tunnel did not affect free field response at dimensionless period greater than 10. Subsequent parametric study demonstrated that the amount of amplifications were mainly controlled by dimensionless period, dimensionless depth and flexibility ratio. Tunnel effect on the amplification pattern is more prominent for dimensionless period between 3 to 10, flexibility ratio greater than 1 and dimensionless depth less than 3. The study revealed that subway tunnel influences the seismic response of low period buildings, constructed above the tunnel.     

Experimental validation of a numerical prediction model for free field traffic induced vibrations by in situ experiments

This paper deals with the validation of a numerical model for traffic induced vibrations. Road unevenness subjects the vehicle to vertical oscillations that cause dynamic axle loads, which generate waves propagating in the subsoil. A 2D vehicle model is used for the calculation of the axle loads from the longitudinal road profile. The free field soil response is calculated with the dynamic Betti–Rayleigh reciprocity theorem, using a transfer function between the road and the receiver that accounts for dynamic road–soil interaction. The validation relies on the measured response of the vehicle's axles and the soil during the passage of a truck on an artificial unevenness with speeds varying from 30 to 70 km/h. The agreement between the numerical and the experimental results is good: the influence of the vehicle speed and the distance from the road is well predicted, while the ratio of the predicted and the measured PPV is less than two.     

Field experiment and numerical study on active vibration isolation by horizontal blocks in layered ground under vertical loading

In this paper, a series of field experiments were carried out to investigate the active vibration isolation for a surface foundation using horizontal wave impedance block (WIB) in a multilayered ground under vertical excitations. The velocity amplitude of ground vibration was measured and the root-mean-square (RMS) velocity is used to evaluate the vibration mitigation effect of the WIB. The influences of the size, the embedded depth and the shear modulus of the WIB on the vibration mitigation were also systematically examined under different loading conditions. The experimental results convincingly indicate that WIB is effective to reduce the ground vibration, especially at high excitation frequencies. The vibration mitigation effect of the WIB would be improved when its size and shear modulus increase or the embedded depth decreases. The results also showed that the WIB may amplify rather than reduce the ground vibration when its shear modulus is smaller or the embedded depth is larger than a threshold value. Meanwhile, an improved 3D semi-analytical boundary element method (BEM) combined with a thin layer method (TLM) was proposed to account for the rectangular shape of the used WIB and the laminated characteristics of the actual ground condition in analyzing the vibration mitigation of machine foundations. Comparisons between the field experiments and the numerical analyses were also made to validate the proposed BEM.     

Full-scale model testing on a ballastless high-speed railway under simulated train moving loads

Model testing in laboratory, as an effective alternative to field measurement, provides valuable data to understand railway׳s dynamic behaviors under train moving loads. This paper presents comprehensive experimental results on track vibration and soil response of a ballastless high-speed railway from a full-scale model testing with simulated train moving loads at various speeds. A portion of a realistic ballastless railway comprising slab track, roadbed, subgrade, and subsoil was constructed in a larger steel box. A computer-controlled sequential loading system was developed to generate equivalent vertical loadings at the track structure for simulating the dynamic excitations due to train׳s movements. Comparisons with the field measurements show that the proposed model testing can accurately reproduce dynamic behaviors of the track structure and underlying soils under train moving loads. The attenuation characteristics of dynamic soil stresses in a ballastless slab track is found to have distinct differences from that in a ballasted track. The model testing results provide better understanding of the influence of dynamic soil–structure interaction and train speed on the response of track structure and soils.     

地铁交通对某实验楼的环境振动的模拟分析

在地铁隧道附近,对于环境振动要求较高的特殊建筑物和精密仪器,地铁列车走行时引起的振动影响不容忽视。基于动力反应分析理论,通过建立有限元模型,并以实际测得的列车走行时地铁和轻轨在路基附近的加速度波形作为振动输入,模拟分析了正在规划修建的北京地铁8号线开通后将对附近某实验大楼内仪器可能造成的振动影响,同时对实验楼附近地铁振动的衰减规律进行了初步分析,为实验楼和仪器台是否应采取避振措施提供了参考依据。     

无砟轨动车组运行激励场地振动谱分析

为研究CRH2动车组在无砟轨道段运行引起的场地加速度振动的频谱特性,本文对我国首条无砟轨道段(渝遂铁路二岩隧道—湾里头隧道段)动车组运行时的场地振动进行了现场实测;对实测竖向振动加速度时程进行1/3倍频谱分析表明:地面竖向振动加速度随着与振源距离的增大而明显衰减,随车速增大场地振动强度增强;应用正交HHT变换,对加速度时程进行了Hilbert谱分析,获得了地面竖向振动加速度的主频为10~120Hz、振动传播高频成分衰减较快等频谱特性;最后,将Hilbert边际谱与傅里叶谱进行了对比分析,得到了两种方法分析振动信号频谱特性表现出的差异性。     

Influence of water saturation on horizontal and vertical motion at a porous soil interface induced by incident P wave

This paper describes a study on the influence of water saturation on horizontal and vertical motion at the interface between porous soil and rock formation due to an incident P wave. The soil is modeled as a partially water-saturated porous material with a small amount of air inclusions, while the underlying rock is approximately regarded as an ordinary one-phase solid. Theoretical formulation is developed for the computation of motion amplitudes in both horizontal and vertical components, which are considered as functions of the degree of saturation, the angle of incidence as well as the frequency. Numerical results are provided to illustrate the effect of saturation on displacement amplitudes in both components and their ratios. The results show that even a slight decrease of complete saturation may lead to a substantial change in the motion amplitudes in both horizontal and vertical components. In general, partial saturation may cause lower horizontal-to-vertical ratios over the entire range of incident angles except the normal incidence, implying the potential importance of saturation effects in the interpretation of field observations.