David Connolly

Railway-induced ground vibrations - a review of vehicle effects

This paper is a review of the effect of vehicle characteristics on ground- and track borne-vibrations from railways. It combines traditional theory with modern thinking and uses a range of numerical analysis and experimental results to provide a broad analysis of the subject area. First, the effect of different train types on vibration propagation is investigated. Then, despite not being the focus of this work, numerical approaches to vibration propagation modelling within the track and soil are briefly touched upon. Next an in-depth discussion is presented related to the evolution of numerical models, with analysis of the suitability of various modelling approaches for analysing vehicle effects. The differences between quasi-static and dynamic characteristics are also discussed with insights into defects such as wheel/rail irregularities. Additionally, as an appendix, a modest database of train types are presented along with detailed information related to their physical attributes. It is hoped that this information may provide assistance to future researchers attempting to simulate railway vehicle vibrations. It is concluded that train type and the contact conditions at the wheel/rail interface can be influential in the generation of vibration. Therefore, where possible, when using numerical approach, the vehicle should be modelled in detail. Additionally, it was found that there are a wide variety of modelling approaches capable of simulating train types effects. If non-linear behaviour needs to be included in the model, then time domain simulations are preferable, however if the system can be assumed linear then frequency domain simulations are suitable due to their reduced computational demand.

The growth of railway ground vibration problems — A review

Ground-borne noise and vibration from railway lines can cause human distress/annoyance, and also negatively affect real estate property values. Therefore this paper analyses a collection of technical ground-borne noise and vibration reports, detailing commercial vibration assessments undertaken at 1604 railway track sections, in 9 countries across the world. A wide range of rail projects are considered including light rail, tram lines, underground/tunnelled lines, freight, conventional rail and high speed rail. It documents the rise in ground-borne vibration problems and trends in the prediction industry, with the aim of informing the current research area. Firstly, the reports are analysed chronologically and it is found that railway vibration is a growing global concern, and as such, assessments have become more prevalent. International assessment metrics are benchmarked and it is found that velocity decibels (VdB), vibration dose value (VDV) and peak particle velocity (PPV) are the most commonly used methods of assessment. Furthermore, to predict vibration levels, the physical measurement of frequency transfer functions is preferential to numerical modelling. Results from the reports show that ground vibration limits are exceeded in 44% of assessments, and that ground-borne noise limits are exceeded in 31%. Moreover, mitigation measures were required on approximately 50% of projects, revealing that ground-borne noise and vibration is a widespread railroad engineering challenge. To solve these problems, the most commonly used abatement strategy is a modification of the railtrack structure (active mitigation), rather than the implementation of a more passive solution in the far-field.

Railway ground vibrations induced by wheel and rail singular defects

Railway local irregularities are a growing source of ground-borne vibration and can cause negative environmental impacts, particularly in urban areas. Therefore, this paper analyses the effect of railway track singular defects (discontinuities) on ground vibration generation and propagation. A vehicle/track/soil numerical railway model is presented, capable of accurately predicting vibration levels. The prediction model is composed of a multibody vehicle model, a flexible track model and a finite/infinite element soil model. Firstly, analysis is undertaken to assess the ability of wheel/rail contact models to accurately simulate the force generation at the wheel/rail contact, in the presence of a singular defect. It is found that, although linear contact models are sufficient for modelling ground vibration on smooth tracks, when singular defects are present higher accuracy wheel/rail models are required. Furthermore, it is found that the variation in wheel/rail force during the singular defect contact depends on the track flexibility, and thus requires a fully coupled vehicle/track/foundation model. Next, a parametric study of ground vibrations generated by singular rail and wheel defects is undertaken. Six shapes of discontinuity are modelled, representing various defect types such as transition zones, switches, crossings, rail joints and wheel flats. The vehicle is modelled as an AM96 train set and it is found that ground vibration levels are highly sensitive to defect height, length and shape.

Train speed calculation using ground vibrations

This paper presents a high precision train speed calculation technique based on ground vibration information. This versatile method can calculate speeds for trams, intercity locomotives and high speed trains on any track/embankment arrangement. Additionally, it has high accuracy for sensors located up to 100 m from the track, thus allowing semi-remote, non-invasive monitoring of train velocities. The calculation method combines three separate speed calculation techniques to provide estimates for arbitrary train speeds, even for sensors placed at large track offsets. The first estimation technique involves the use of cepstral analysis to isolate key harmonics for use with speed calculation. The second method is similar; however, the combination of a running rms and a previously developed “dominant frequency method” are used. The third method uses an analytical vibration frequency prediction model in combination with regression analysis to calculate train speed. All three methods are combined into one calculation procedure, resulting in high accuracy estimates. To show the robustness and ability of the new method to calculate a wide range of train speeds, it is used to predict tram, intercity and high speed rail train passage velocities generated from a previously validated vibration prediction numerical model. More importantly, it is used to predict train speeds during field trials performed on operational railway lines in Belgium and in UK. The new method is shown to offer high performance for several train types and track setups (including abutment and tunnel cases).

The influence of train properties on railway ground vibrations

This paper uses a sensitivity analysis to quantify the dominant train properties (mass and spacing of wheels and bogies) that contribute to ground-borne vibration generation, with the aim of reducing the complexity of train–track numerical models. This research is significant because ground-borne vibration from railways is a growing problem, particularly in urban areas. Despite this fact, attempting to predict vibration levels is complex because there are many variables that contribute to the overall dynamic response. Therefore, a deterministic approach is commonly used, that ignores many of these variables. Thus, this paper identifies the variables that can be ignored, while highlighting those that are highly influential on vibration generation. For this purpose, a previously validated 2.5D finite elements-boundary elements approach is used to simulate dynamic train–track interaction. It is computed many times for a variety of modelling variables to investigate the effect of each on the ground-borne vibration levels in the far field. It is found that increases in unsprung mass of the train causes a large increase in vibration levels. Furthermore, changes in wheel/bogie spacing and semi-sprung mass are found to have a minimal effect on vibration generation.

Geohazard detection and other applications of chimney cubes

The “chimney cube” is a new processing and interpretation tool that highlights vertical anomalies on seismic data associated with gas clouds and gas chimneys. They are used to address drilling hazards caused by shallow gas pockets and platform stability problems due to subsea mud volcanoes. Chimney cube data also assist exploration of hydrocarbon targets by high grading prospects and improving understanding of the petroleum system.

Railway cuttings and embankments: Experimental and numerical studies of ground vibration.

Railway track support conditions affect ground-borne vibration generation and propagation. Therefore this paper presents a combined experimental and numerical study into high speed rail vibrations for tracks on three types of support: a cutting, an embankment and an at grade section. Firstly, an experimental campaign is undertaken where vibrations and in-situ soil properties are measured at three Belgian rail sites. A finite element model is then developed to recreate the complex ground topology at each site. A validation is performed and it is found that although the at-grade and embankment cases show a correlation with the experimental results, the cutting case is more challenging to replicate. Despite this, each site is then analysed to determine the effect of earthworks profile on ground vibrations, with both the near and far fields being investigated. It is found that different earthwork profiles generate strongly differing ground-borne vibration characteristics, with the embankment profile generating lower vibration levels in comparison to the cutting and at-grade cases. Therefore it is concluded that it is important to consider earthwork profiles when undertaking vibration assessments.

Modelling the Environmental Effects of Railway Vibrations from Different Types of Rolling Stock: A Numerical Study

This paper analyses the influence of rolling stock dynamics on ground-borne vibration levels. Four vehicle types (Thalys, German ICE, Eurostar, and Belgian freight trains) are investigated using a multibody approach. First, a numerical model is constructed using a flexible track on which the vehicles traverse at constant speed. A two-step approach is used to simulate ground wave propagation which is analysed at various distances from the track. This approach offers a new insight because the train and track are fully coupled. Therefore rail unevenness or other irregularity on the rail/wheel surface can be accurately modelled. Vehicle speed is analysed and the frequency spectrums of track and soil responses are also assessed to investigate different excitation mechanisms, such as carriage periodicities. To efficiently quantify train effects, a new (normalised) metric, defined as the ratio between the peak particle velocity and the nominal axle load, is introduced for a comparison of dynamic excitation. It is concluded that rolling stock dynamics have a significant influence on the free field vibrations at low frequencies, whereas high frequencies are dominated by the presence of track unevenness.

Interpretation of gas chimney volumes

In this paper we describe how seismically derived gas chimneys can be used to determine hydrocarbon migration paths. The emphasis will be on how to interpret chimney cubes. Through several case history examples, we will show chimney cubes can reveal vertical hydrocarbon migration paths that can be interpreted from their source into reservoir traps all the way to the surface. We will highlight distinguishing features of chimneys for oil-prone versus gas-prone prospects, and those related to separating active fault migration pathways. Further, we will show chimneys can support charging of shallow reservoirs. Our understanding of the petroleum system can improve by combining gas chimney data with other information. As such a chimney cube can be seen as a new exploration tool.

Use of conventional site investigation parameters to calculate critical velocity of trains from Rayleigh waves

This paper presents a practice-ready approach to calculating railway track critical velocity from Rayleigh waves and ground-borne vibrations with conventional site investigation parameters. Types of ground waves are discussed; equations define the wave velocities mathematically. Relationships between the terms in the equations defining Rayleigh wave velocity and hence track critical velocity are established. The reader can undertake these calculations from a standard low-cost site investigation. The design train critical velocity may be restricted to 0.7 3 Rayleigh wave velocity. However, the track critical velocity is in the region of 1.1 to 1.3 3 Rayleigh wave velocity.