The aim of this research is to develop a fuller understanding of the mechanical behaviour of the sleeper/ballast interface, related in particular, to the forces applied by high speed tilting trains on low radius curves. The research has used literature review, field measurements, and laboratory experiments on a single sleeper bay of track. Theoretical calculations are also presented. Field measurements are carried out using geophones to record time/deflection for sleepers during passage of Pendolino trains on the West Coast Main Line. Calculations are presented to quantify normal and extreme magnitudes of vertical, horizontal and moment (VHM) loads on individual sleepers. Results from laboratory experiments, on the pre-failure behaviour of the sleeper to ballast base contact area, show that lateral load/deflection behaviour is load path dependent and relations are determined for improved computer modelling of the sleeper/ballast interface. Further test results are used to establish the failure envelopes for combined VHM loading of the sleeper/ballast base contact area. Tests show that the sleeper/ballast base resistance at failure occurs at a load ratio (H/V) of about 0.45 (24°) at 2 mm of displacement tending to 0.57 (30°) at greater displacements. In addition, measurements from pressure plates within the testing apparatus are used to describe the development of confining stress within the ballast during 100 cycles of vertical load. The development of confining stress is assessed with reference to a finite element model of the laboratory apparatus and it is shown that the earth pressure ratio moves towards the active condition for peak load and the passive condition at minimum load per cycle. The contribution to lateral resistance of the crib ballast and varying sizes of shoulder ballast is also established and it is found that the shoulder and crib resistance can best be characterised by taking the mean resistance over a range of deflection from 2 mm to 20 mm. Calculations are presented, supported by the experimental data, to quantify the resistance from different sizes of shoulder ballast and a chart is presented which can be used as the basis for shoulder specification in practice.

For application in damping treatments, elastomeric materials should have a high damping loss factor, but this is inevitably linked to a strong temperature-dependence of the dynamic properties. A methodology is developed that allows a material to be formulated for a particular damping application where temperature-dependence has to be taken into account. The methodology is applied to the case of a tuned absorber system used for damping the vibration of a railway track. This is required to be effective over a temperature range -20°C to 40°C. To investigate the effect of the temperature on the performance of a rail damper, a simple Timoshenko beam model of the track vibration is used, to which are added single-frequency and dual-frequency tuned absorbers. The results show that a high noise reduction can be achieved for the optimum stiffness, provided that the loss factor is between about 0.25 and 0.4. In order to study the generic effects of high damping versus constant stiffness, the time-temperature superposition principle is used to convert frequency-dependence to temperature-dependence for a notional material with constant loss factor. This is used in the prediction of decay rates and thereby noise reduction. In addition, a weighted noise reduction is studied by using measured rail temperature distributions. This temperatureweighted noise reduction allows a single number measure of performance to be obtained which can be used to assess various elastomeric materials in order to determine the optimum material for a given situation. Two types of viscoelastic material, butyl and EPDM rubbers with various amount of fillers and plasticisers are investigated. The properties of both rubbers have been measured over the range of temperatures for frequencies 300-3000 Hz. For this a test rig had to be modified. For butyl, the best combination of filler and plasticiser gives temperature weighted noise reductions up to 5.9 dB(A). Butyl rubber is suitable for use in the rail absorber giving high noise reductions between 0°C and 40°C. The best EPDM compound gives a temperature-weighted noise reduction up to 6.2 dB(A). Comparing these two rubbers, EPDM is more suitable for low temperatures below 10°C and butyl is more suitable for higher temperatures above 10°C.

A model of the development of rail-head acoustic roughness on tangent track has been formulated. The model consists of a two-dimensional time domain wheel-rail interaction force calculation, with the normal force used as the input to a two-dimensional rolling contact and wear model. The possibility of multiple wear mechanisms arising from stress concentrations is considered by using a wear coefficient that can vary with the conditions at each point in the contact. The contact model is based on a variational technique, taking account of non-Hertzian and transient effects. A novel feature of the rolling contact model is the introduction of a velocity-dependent friction coefficient. In rolling contact this leads to a high frequency stick-slip oscillation in the slip zone at the trailing edge. Roughness development depends on the dynamics of the track. Roughness growth has often been linked to the pinned-pinned frequency and other resonances of the coupled track and vehicle system. Here the effect of different vehicle and track parameters on track dynamics, wear and roughness development has been examined. Rail dampers are studied as they change the dynamic response of the track. Results are presented in the form of roughness growth rate functions both for individual vehicle types and for mixed traffic. The model parameters match those at a site used for measurements of roughness development taken by Deutsche Bahn AG as part of the EU project Silence. The study shows that it is important to include non-Hertzian effects when studying roughness with wavelengths shorter than 100 mm. With a non-Hertzian contact model, no mechanism has been found for consistently increasing roughness levels. The model predicts that roughness wavelengths shorter than the contact length will wear away. Rail dampers are shown to reduce the pinned-pinned frequency and smooth the peaks and troughs in the track receptance. Rail dampers also reduce the dynamic wheel-rail interaction forces, especially around the pinned-pinned resonance, and shift the force spectrum to lower frequencies or longer wavelengths. However, rail dampers are not predicted to affect roughness growth rates significantly.

Passengers of land transport are exposed to horizontal and rotational oscillations at frequencies less than 1 Hz which may cause vibration discomfort and motion sickness. Previous knowledge of human responses to motion is insufficient for predicting the discomfort caused by low frequencies. The objective of this thesis is to improve understanding of subjective responses to lateral and roll oscillation (presented in isolation and in combination) at frequencies less than 1 Hz in order to establish a predictive model of comfort. The first of five experiments tested the predictions of a conceptual model of motion sickness. Illness ratings were obtained over a 30-minute exposure to 0.2 Hz fully roll-compensated lateral oscillation where the point of full roll-compensation was either at the seat surface (i.e. ‘seat compensation’) or at head height (i.e. ‘head compensation’). Median illness ratings were greater during ‘head compensation’, showing some support for the motion sickness model, but differences were not statistically significant. Age, stature and body weight had no effect on illness ratings, but Asians were more than three-times as likely to experience ‘mild nausea’ than Europeans. It is concluded that differences in the position of full roll-compensation in transport vehicles are less important for motion sickness than inherent differences in passenger populations. The next four experiments used the method of magnitude estimation to determine the vibration discomfort caused by lateral oscillation, roll oscillation, and fully roll-compensated lateral oscillation with a variety of seating configurations. In the second experiment, lateral acceleration between 0.2 and 1.0 Hz caused less discomfort when sitting with a backrest than when sitting without a backrest on both a rigid seat and on a cushioned train seat; contrary to the predictions of current standards. In the third experiment, 0.25 to 0.4 Hz lateral acceleration in the plane of the seat caused similar discomfort regardless of whether the acceleration was due to lateral oscillation or roll oscillation through the gravitational vector, but above 0.4 Hz, discomfort from the roll was far greater. At frequencies less than 0.5 Hz, fully compensating the lateral acceleration with roll improved comfort compared to uncompensated lateral acceleration, but at greater frequencies, roll-compensation worsened comfort and caused discomfort similar to pure roll oscillation at 1 Hz. The fourth and fifth experiments examined differences in discomfort caused by the rigidity of the seat pan and the height of the backrest. In the fourth experiment, discomfort was greater on a soft foam seat than on a rigid seat during lateral oscillation below 0.63 Hz, during roll oscillation below 0.5 Hz and during fully roll-compensated lateral oscillation between 0.315 and 0.5 Hz. In the fifth experiment, discomfort was greater without a backrest than with a short backrest for lateral oscillation between 0.315 and 0.5 Hz. Contrary to current standards, discomfort was also greater without a backrest than with a high backrest for lateral oscillation below 1 Hz and for roll oscillation below 0.5 Hz. In addition, sitting with a backrest was beneficial for comfort with fully roll-compensated lateral oscillation between 0.4 and 0.63 Hz. The results of the five experiments were collated to provide recommendations for the improvement of current vibration standards. On the basis of experiment 1, a new multiplying factor for the prediction of vomiting incidence in an unadapted group of male Asian adults is offered. On the basis of the four discomfort experiments, modifications to current frequency weightings for lateral acceleration and roll acceleration are offered so as to extend the prediction to frequencies less than 0.5 Hz. Guidance for the prediction of discomfort with fully roll-compensated lateral oscillation is also provided. The thesis is concluded with recommendations for future research.

The aerodynamic noise produced by train pantographs and bogies is significant for typical speeds of modern high-speed trains. In order to reduce the negative environmental impact of high-speed train noise, the aerodynamic noise should be tackled in an early stage of the train design. In recent years, Computational Fluid Dynamics (CFD) and Computational AeroAcoustics (CAA) models have been developed in order to predict aerodynamic noise but they are very computationally-intensive. In this thesis, a semi-empirical component-based model is developed for quick prediction of the aerodynamic noise radiated by a high-speed train pantograph and bogie. The overall noise from the pantograph and bogie is obtained as the incoherent sum of the contributions predicted from the individual components. The model empirical constants are obtained using an experimental database built from data found in the literature and noise tests carried out during this work to evaluate the effect of different geometries and inflow conditions. For the pantograph, the struts are approximated as cylinders with a particular cross-section. To extend the available database, anechoic wind tunnel noise tests were carried out using cylinders with different cross-sections for different configurations. The predictions are compared with available noise measurements using a full-size pantograph showing good agreement. For the bogie case, the prediction model is developed by identifying each of the bogie components with simple shapes. Anechoic wind tunnel noise measurements were carried out using simple shapes to determine the empirical constants of the model. Additionally, scale train car body and bogie mock-ups were used, allowing for model validation and also providing useful information on the dependence on different factors of the aerodynamic noise generation in the bogie region. The results show the potential of the model to be used as an engineering tool to predict aerodynamic noise from train pantographs and bogies, allowing the effect of design modifications of components to be assessed and low-noise technology to be developed.

The aim of the research was to improve the fundamental understanding of mechanical behaviour of ballast and study the effect of tamping on ballast. The experiments were carried out on scaled railway ballast to eliminate the difficulties associated with testing large particle granular materials. Consideration was given to the gradation, mineralogy and shape during scaling. Particle characterisation work was carried out on scaled and full size ballast using imaging techniques to examine the validity of the use of scaled ballast. Detailed analysis of results is used to quantitatively measure the changes in shape with particle size. The results show measurable differences in particle shape between different particle size intervals. As the differences are small in magnitude, they do not invalidate the use of scaled ballast. Monotonic, cyclic experiments were carried out as part of a laboratory testing programme. Scaled ballast shows generally similar stress strain behaviour to larger granular materials. The friction angle of 40o to 50o for the confining pressure range of 15 kPa to 200 kPa falls within the range of friction angle obtained for full size ballast in the literature. The effect of changing confining pressure during train loading was examined. The results show that the settlement increases and the stiffness reduces when the confining pressure cycles. The effect of principal stress reversal during tamping was examined by an extension stage after the cyclic loading. It is shown that massive settlement occurs after the extension stage during initial cycles and settlement returns back to the pre-extension stage soon under loading. The results evidence the disruption of ballast structure and loss of stiffness due to tamping. Specimens were resin stabilised within the triaxial cell after specific stress paths had been followed. The changes in structure during a specific stress path can be studied by CT examination.

For high-speed trains, aerodynamic noise becomes significant when their speeds exceed 300 km/h and can become predominant at higher speeds. Since the environmental requirements for railway operations will become tighter in the future, it is necessary to understand the aerodynamic noise generation and radiation mechanism from high-speed trains by studying the flow-induced noise characteristics to reduce such environmental impacts. The aim of this thesis is to investigate the flow behaviour and the corresponding aeroacoustic mechanisms from high-speed trains, especially around the bogie regions. Since the prediction of the flow-induced noise in an industrial context is difficult to achieve, this study focuses on scale models with increasing complexity. The aerodynamic and aeroacoustic behaviour of the flow past an isolated wheelset, two tandem wheelsets, a simplified bogie and the bogie inside the cavity with and without the fairing as well as considering the influence of the ground are investigated at a scale 1:10. A two-stage hybrid method is used consisting of computational fluid dynamics and acoustic analogy. The near-field unsteady flow is obtained by solving the Navier-Stokes equations numerically through the delayed detached-eddy simulation and the source data are applied to predict the far-field noise signals using the Ffowcs Williams-Hawkings acoustic analogy. All simulations were run with fully structured meshes generated according to the guidelines based on a grid independence study on a circular cylinder case. Far-field noise radiated from the scale models was measured in an open-jet anechoic wind tunnel. Good agreement is achieved between numerical simulations and experimental measurements for the dominant frequency of tonal noise and the shape of the spectra. Numerical results show that turbulent flow past the isolated wheelset is dominated by three-dimensional vortices. Vortex shedding around the axle is the main reason for the tonal noise generation with the dominant peak related to the vortex shedding frequency. The noise directivity shows a typical dipole pattern. Moreover, for both the tandem-wheelset and the simplified bogie cases, the unsteady flow developed around them is characterized by the turbulent eddies with various scales and orientations including the coherently alternating shedding vortices generated from the upstream axles. The vortices formed from the upstream geometries are convected downstream and impinge on the downstream bodies, generating a turbulent wake behind the objects. Vortex shedding and flow separation as well as interaction around the bodies are the key factors for the aerodynamic noise generation. The radiated tonal noise corresponds to the dominant frequencies of the oscillating lift and drag forces from the geometries. The directivity exhibits a distinct dipole shape for the noise radiated from the upstream wheelset whereas the noise directivity pattern from the downstream wheelset is multi-directional. Compared to the wheelsets, the noise contribution from the bogie frame is relatively small. Furthermore, when the bogie is located inside the bogie cavity, the shear layer developed from the cavity leading edge has a strong interaction with the flow separated from the upstream bogie and cavity walls. Thus a highly irregular and unsteady flow is generated inside the bogie cavity due to the considerably strong flow impingement and interaction occurring there. Unlike the isolated bogie case, noise spectra from the bogie inside the cavity are broadband and a lateral dipole pattern of noise radiation is generated. The noise prediction based on the permeable surface source is formulated and programmed using the convective Ffowcs Williams-Hawkings method. Results show that the bogie fairing is effective in reducing the noise levels in most of the frequency range by mounting a fairing in the bogie area; and for the bogie inside the bogie cavity with the ground underneath, the far-field noise level is increased due to more flow interactions around the geometries and the ground reflection effect.

Despite compacted soils being unsaturated, geotechnical design is predominantly based on saturated soils, despite it being known that differences exist between the behaviour of saturated and unsaturated soils. Suction in soils has been shown to increase its strength and stiffness with the increase dependent on the degree of suction, soil type and particle arrangement. Future climate change predictions suggest an increase in average global temperatures leading to longer drier summers and wetter winters resulting in seasonal fluctuations in suction, such that unsaturated soil behaviour will become more important. Transport infrastructure such as railway tracks, founded at shallow depths, are likely to be unsaturated and influenced by variations in suction. A key parameter in assessing the performance of soils is stiffness; in particular shear modulus, however, although suction affects shear modulus, limited research has been conducted into its influence. This research, therefore, considers how variations in suction influence the small strain shear modulus of railway formation material. Soil water characteristic curves were determined, using the pressure plate apparatus and filter paper technique, for four materials covering the spectrum of railway formation materials encountered on the COALlink line in South Africa. Shear modulus measurements of specimens prepared from two of these materials were determined using a Stokoe resonant column apparatus. Suction was controlled by preparing specimens at different water contents, with the suction independently measured using the filter paper technique. Results showed that shear modulus was significantly influenced by suction and exhibited a complex behaviour. For specimens tested at their preparation water content shear modulus increased with increasing suction up to an optimum value, and then reduced as suctions exceeded this optimum value forming a bell-shaped curve. The influence of suction was seen to be greater at lower net normal stresses. Although this behavioural pattern was similar for both materials tested in the resonant column apparatus, the peak value of shear modulus increased with clay content. Importantly, the marked changes in shear modulus due to suction coincided with the suction range predicted in-situ. Tests were also conducted on specimens prepared at different water contents but the same density, airdried to very low water contents. The shear moduli of these air dried specimens were markedly higher than those of the dry and unsaturated specimens tested at their preparation water contents. Variation in measured shear modulus between specimens led to the conclusion that different particle arrangements between the specimens may have also contributed to the changes in shear modulus and were dependent on the preparation water content. At high water contents the clay particles became evenly distributed around the sand particles when the specimen was prepared, whilst, at low water contents the clay formed lumps during preparation of the material mix and became embedded with the sand particles during formation. CT scanning undertaken to look at the particle arrangement highlighted regions throughout the specimen where sand particles were embedded in lumps of clay and silt particles. These results are the first to demonstrate the importance of suction and its variation on the small strain shear modulus behaviour of railway formation material.

This thesis adopts a holistic approach towards railway track capacity to develop methodologies for different aspects of defining, measuring, analysing, improving and controlling track capacity utilisation. Chapter 1 presents an overview of the concept of capacity and the railway capacity challenge is explained. Chapter 2 focuses on past approaches to defining and analysing the concept of railway capacity. Existing methods for estimating capacity utilisation are studied in four categories: analytical methods, parametric models, optimisation and simulation. Chapter 3 examines various factors affecting capacity utilisation. Chapter 4 develops the systems engineering foundation toward railway capacity. From process improvement methods, Six Sigma and its Define, Measure, Analyse, Improve and Control (DMAIC) cycle is chosen as the underlying framework of the thesis. Chapter 5 defines lean, micro and macro capacity utilisation based on the discrete nature of railway capacity. Data Envelopment Analysis (DEA) is used to develop two novel methodologies to analyse lean capacity utilisation. A DEA model analyses relative efficiency of train operating companies based on their efficiency to transform allocated train paths (timetabled train kilometres) and franchise payments to passenger-kilometres while avoiding delays. A case study demonstrates its application to 16 train operating companies in the UK. The operational efficiency of stations is benchmarked from similar studies for ports and airports. Two models are developed for analysing technical efficiency and service effectiveness. 96 busiest stations in Great Britain are analysed by this method. For analysing capacity utilisation in the freight sector, the concept of ‘profit-generating capacity’ is introduced in chapter 6. It is applied in an American freight case study to choose between bulk and intermodal trains in a heterogeneous traffic. DEA is also used in another case study for identifying the most profitable commodities. Chapter 7 suggests using variation reduction and failure mode and effect analysis (FMEA) to control capacity utilisation. For improving railway capacity utilisation it is suggested to find and improve the weakest line section, the weakest trains and the weakest station. A real world case study of the South West Main Line in Great Britain, demonstrates applying these aspects. For finding the weakest line section two existing methods of the UIC 406 and the CUI method are compared with each other. For finding the weakest trains a meso index is suggested. It can identify which trains can be removed to free up some capacity in the busiest section of the line. Simulating delays and removing the highest delay causing trains is another method suggested. The weakest stations are identified by applying the DEA methodology developed in chapter 5. Target values for train stops at each station are suggested to be fed to the tactical timetabling. It is concluded that developing methodologies to analyse, improve and control railway capacity utilisation is needed and the methodologies proposed in this thesis can be a stepping stone towards them.

Ballast is a primary component of the railway track and it has several functions including the ability to resist vertical, lateral and longitudinal forces applied to the sleepers from the train wheels. In response to the stresses induced during a train passage, ballast typically experiences plastic settlement which can reach unacceptable magnitudes. Thus, ballast is the focus of the majority of maintenance and renewal activities. In response to the growing need for resilient track materials (including ballast) to cope with increasing train speed, load and frequency, means of optimizing its performance and minimizing maintenance requirements are required. Ballast improvement techniques, such as the use of geogrids, have attracted a great deal of attention in terms of research, but huge potential for reducing costs through ballast improvement still exist. It has been shown from previous research that the use of randomly oriented fibres in sands can significantly improve their strength. This technique might be used to improve ballast strength and reduce track geometry deterioration. In addition, fibre reinforcements in ballast can potentially provide a new method of reinforcing ballast whilst maintaining the capability of withstanding typical tamping operations which are incompatible with geogrids. However, there is a lack of rigorous scientific understanding of the effects of fibre reinforcements on relatively large aggregates such as railway ballast. This research examines the effect of random fibre inclusions on the packing structure of granular materials (coarse sand and scaled ballast) and describes the physical implications associated with the observed changes. The mechanical properties of fibre reinforced granular materials across different particle sizes and a hypothesis of fibre/particle reinforcement suitable for relatively large particles are presented. An image-based deformation measurement technique has also been used to investigate the effects of fibre reinforcements on the local deformation of triaxial specimens to corroborate the observed mechanical behaviour of the reinforced specimens. Finally, the mechanical behaviour of a fibre reinforced ballast layer below a cyclically loaded railway sleeper was investigated using a full scale laboratory tests.