In this thesis, the main objective is to identify the resilient deformation behaviour of rail trackbed especially in ballast and calculate the stress distribution. A purpose-designed three dimensional Finite Element railway trackbed model is presented in which linear elastic behaviour is assumed in all parts of the model. The study has also evaluated the effects of different variables including moving load magnitude, loading speed and stiffness of materials on stress conditions and deflections based. A comprehensive literature review on a wide background of railway trackbed has been carried out. Railway ballast specifications, deformation mechanisms, resilient and permanent deformation behaviour of granular material, introduction of fouling material and its influence on ballast behaviour are explained to provide the basis for trackbed analysis. Results show that a higher vertical displacement underneath the sleeper may occur when the loading speed is higher than 120km/h. Also, higher speed and Young’s modulus of ballast can result in higher damaging stresses. A stiffer subgrade can result in less rotation of sleeper. A significant effect of subgrade stiffness on stress paths and rotation of sleeper can only be found when Young’s modulus of subgrade is in a low level. Stiffer rail pad can lead ballast element get cracked more easily. Softer pad results in less damaging stresses. In addition, there is no obvious change of either the stress ratio or sleeper rotation as stiffness of the ballast increased.

Maintenance management decision-support systems are needed to help senior decision-makers and asset managers to better plan timely and efficient maintenance. Within the railway industry, several maintenance management decision-support systems have been developed. However, most these operate at project level where decisions are limited to short sections of track. Network level maintenance management systems enable future prediction of the condition of the railway network under different allocation of resources in a manner to provide acceptable levels of safety, reliability and cost. This project describes the development of a theoretical framework for the strategic assessment of network level railway maintenance funding and policy decisions. The model is designed to aid railway asset managers in planning medium to long-term maintenance investment requirements for the railway network. The model is based on stochastic processes which are capable of determining the effects of traffic, maintenance and climate on network condition under any budget scenario.

Ballasted track represents by far the most used infrastructure for railway transportation system, its main benefits being the relatively low construction costs, the maintainability, the relatively high damping capacity, noise absorption and high flexibility, the self-adjusting properties and high hydraulic conductivity. These are related to the structure of ballast layer as assembly as well as to particle properties. However, the unbound nature of ballast layer is also responsible for the reduction of geometric quality of the track, and therefore, its safety and ride comfort. The passage of trains causes cyclic movements of the unbound particles that result in permanent vertical and lateral deformations. For this track form, vertical settlement of granular layers and ballast particles degradation represent the major problems, affecting frequency of maintenance and track durability. In this context, reducing minor and major maintenance frequency while effectively using available resources by developing innovative technologies is a challenge for current and future railway research. After reviewing the most relevant existing solutions to improve ballasted track-bed behaviour and main factors affecting their performance, the aim of this research was to investigate the possibility of stabilising ballast with bitumen emulsion, as novel solution to slow down the loss in track quality associated with ballast settlement and particle degradation. In this regard, firstly the feasibility of the proposed alternative and main factors affecting its performance have been assessed through model-scale testing (small-scale Precision Unbound Material Analyser - PUMA). Results showed a good potential for this technology to reduce both the short-term and the long-term permanent deformation. It was also observed that bitumen stabilisation could modify mechanical properties due to the presence of a viscoelastic component (bitumen). The type of emulsion and its dosage played important roles in BSB properties: increasing the dosage of bitumen emulsion provided a better resistance to permanent deformation; increasing the viscosity of bitumen emulsion decreased the percentage of material lost, thereby providing improved stabilisation efficiency. Thus, depending on the field condition a specific bitumen emulsion could be designed to obtain the desired results in terms of BSB behaviour and stabilisation efficiency. At the same time, the use of harder bitumen for BSB seemed to improve the resistance to permanent deformation while polymer modification provided a more stable behaviour over time. Model-scale results provided important guidance on the influence of the factors analysed on the proposed technology. Nevertheless, to understand to what extent BSB could represent a solution to improve sustainability and performance of ballasted track-beds, findings had to be verified at full scale. Thus, full-scale box tests have been employed to assess how this technology could be effectively applied to existing ballasted tracks during maintenance operations and to investigate the practicability and maintainability of the presented technology. Results showed that bitumen stabilisation was more effective when applied at an early stage of ballast life (clean ballast), especially when coupled with tamping, providing a significant decrease to permanent deformation and to deformation rate (long-term behaviour). Nonetheless, in comparison with results obtained at model-scale, a slightly different behaviour of BSB in relation to unbound material was observed. Thus, with the aim of correlating previous model-scale PUMA and full-scale ballast box findings and evaluating long-term performance, full-scale PUMA testing was carried out. Results on clean ballast indicated that scale factor instead of the test type was the main factor controlling the effectiveness of Bitumen Stabilised Ballast (BSB) in terms of permanent deformation reduction. On the other hand, results obtained when using lower size aggregate confirmed that increasing the number of contact points increases also the influence of viscoelastic properties given by the bitumen, indicating that the use of different gradations combined with higher dosages (and types) of bitumen emulsions, could potentially modify full-scale track-bed mechanical properties. Key findings obtained from laboratory experiments, consistently showed evidence of the fact that bitumen stabilisation can reduce number of maintenance interventions due to geometry corrections and excessive particle degradation. In this regard, to estimate the environmental and economic impacts of BSB, a performance-based integrated model was developed to predict maintenance strategies of proposed technology in comparison to traditional ballast. This model, by combining the evolution of track irregularities with traffic and the level of contamination of ballast, allowed evaluation of the timing of corrective maintenance activities. Based on these, life-cycle environmental and economic costs of these alternatives have been carried out. Life Cycle Assessment (LCA) results showed that BSB is overall more sustainable than traditional ballasted track, only when considering also its impact on major maintenance operations. Sensitivity analysis carried out showed that BSB advantages are generally higher when the tolerance on the track quality level increases and with heavy traffic lines. LCCA results showed that BSB can provide important savings with respect to traditional ballasted track-bed. Sensitivity analysis showed that BSB would be more profitable for important and congested lines rather than peripheral ones. The influence of carbon conversion factor on results is relatively low while decreasing the discount rate corresponds to higher savings provided by the BSB. Overall, both LCA and LCCA results showed that BSB could offer a more sustainable solution from a life cycle perspective than traditional ballasted track-bed.

Reliability and safety represent key features of any successful railway system and compromising either has undeniable ramifications. Railway industry practitioners are continually challenged to deliver reliability and performance improvements whilst facing ever increasing service demands. These improvements are typically achieved through track maintenance and renewal activities, which have to be balanced against a requirement to reduce whole life-cycle costs. Research focusing on the optimisation of railway track components, which can then be translated to field practice, presents a real opportunity to reduce the frequency of disruptive and often costly track maintenance activities and ultimately prolong the life span of a railway track. A laboratory study of track performance with particular emphasis on railway sleeper type and geogrid type as the main variables has been undertaken. The types of sleepers investigated were the concrete monoblock, twin-block, timber, plastic, and steel sleepers. The geogrids variants tested were the SSLA30 biaxial and TX130 triaxial geogrids with square and triangular apertures respectively. Testing undertaken involved the application of low frequency cyclic loads to railway sleeper sections and full-size sleepers installed on a 300 mm thick ballast with and without geogrid reinforcement. Bending tests, friction tests and hardness tests were initially performed to characterise the material and mechanical properties of the sleepers investigated. Preliminary cyclic tests were conducted with a Box Test apparatus and Composite Element Test (CET) apparatus to approximate field conditions. Full scale tests were subsequently performed with the Nottingham Railway Test Facility (RTF) which is designed to provide a closer representation of field conditions and simulate the passage of an axle load over three sleepers. The outer sleepers in the test facility provided the necessary boundary conditions for the middle sleeper, which was the primary focus of the tests performed. Measures of track performance included vertical track settlement, trackbed stiffness and formation pressure. Additional measurements were made of the differential deflection along the length of the middle sleeper to ascertain if sleeper bending occurred during the tests. Linear elastic and finite element analysis to determine the pressure on top of the subgrade and at the sleeper-ballast interface respectively were performed for idealised sleeper support conditions. The results of the numerical analysis were compared with the RTF pressure plate measurements and estimates of subgrade pressure calculated using empirically derived equations. The results showed that sleeper type influences the permanent settlement that develops in a railway track as well as the magnitude of transient live loads that is transmitted to an underlying subgrade. In line with the permanent settlement results, it is also apparent that trackbed stiffness is a function of sleeper bending stiffness. Measurements of formation pressure and resilient sleeper deflection revealed differences between sleeper types with regards to their ability to retain the as-built geometry of a trackbed, underlining the importance of the sleeper-ballast interface characteristics and sleeper bending stiffness. Traditionally used empirical equations for determining subgrade pressure were found to be conservative compared to subgrade pressures determined using linear elastic analysis and measurements of made of the same using pressure plates in the RTF. Finite element analysis to determine the pressure distributions at the base of different sleepers for a range of support conditions found the shape and magnitude of pressures determined to be consistent with the sleepers’ bending stiffnesses suggesting that sleeper properties should be an important consideration when predicting track performance. The use of the biaxial geogrid installed 100 mm above the base of the ballast reduced permanent settlement for all sleeper types without any significant bias towards any one sleeper type. Additionally, the use of the biaxial geogrid resulted in the delayed deterioration of sleeper support for all sleeper types. The application of the TX130 geogrid resulted in increased settlement and increased deterioration of the as-built trackbed geometry for all sleeper types owing to the grid aperture which proved unsuited to the standard Network Rail ballast gradation. It was proposed that a triaxial geogrid with a larger aperture may offer better results. It was also suggested that sleeper choice that includes consideration for the relative performance of sleeper types is possible for railway practice although it must be commensurate with the intended use of the track with due regard to cost and safety. The research concluded that the concrete monoblock sleeper, which is currently the prevalent sleeper type in the UK (with and without the biaxial geogrid), for the conditions simulated, presents the best opportunity to minimise the maintenance requirements of a railway track.

The use of on-call work in industry has now surpassed that of shiftwork and night work. Industries as a whole make use of on-call work daily as a way to maintain 24/7 operations whilst also reducing costs. Despite this, on-call work remains underresearched and no best practice or management guidelines are available. As the first substantial piece of human factors work examining on-call work in the rail industry, this thesis has the overall aim of increasing the understanding of on-call scheduling systems of work, and also to provide recommendations to the planning and management of on-call work in the rail industry which may also be applied in other industries. A semi-structured interview study with 72 rail maintenance on-call workers of Great Britain rail infrastructure owner and operator (Network Rail) explored on-call arrangements in place and the perceived unwanted consequences of this type of work. Anxiety, fatigue, and reduced well-being were perceived as the main consequences of working on-call. The findings also indicate that when discussing on-call there are three separate on-call situations; being on-call, receiving calls, and responding to calls; which influence the study variables differently. From the key themes identified initially an on-call questionnaire for managerial staff was developed and data from across the country generating 479 individual responses. A two-week diary study (one week on-call and the week after) with 26 participants aimed to collect real-time ratings. Results indicated that working on-call was perceived as a leading cause of stress, poor quality of sleep and fatigue. This is due to the inherent unpredictability of on-call work, which is the key differentiating factor between on-call work and other types of working-hours systems. Receiving and responding to calls were perceived as detrimental to general well-being both to workers and their families, fatigue, and performance. The work performed for this thesis allowed the development of the first on-call specific framework that identifies not only the key factors at play but also the relationships between them. It presents a set of principles or theories that other researchers can use to guide future research and that industry professionals can use to deliver more human friendly on-call work management processes and procedures.

This thesis presents work undertaken in conjunction with Network Rail in the area of planning and re-planning in railway environments. It aimed to study a real world signalling environment to understand the strategies signallers use when re-planning and how decision tools can be designed and integrated into existing signalling environments to support proactive planning. The main research focused on two case studies: A graphical tool developed by signallers to assist in managing station areas; and the rollout and uptake of a graphical time based planning tool. The first case study consisted of interviews and observations investigating how signallers currently plan (in and around station areas) and what existing tools and artefacts are used, followed by an experiment to compare different tools. It was found that signallers who were using a graphical based tool to assist in managing station areas were able manage disruption more efficiently than signallers using a list based tool. The second case study investigated an existing electronic tool called the Train Graph that had already been implemented. Interviews, observations and questionnaires were used to gather data on the opinions and general uptake of the Train Graph. Trust and prior experience were found to be the significant driver of end user behaviour and uptake of the technology. One key output of this research was a tangible framework that can be used by Network Rail to guide design and implementation of future decision support tools and artefacts. The framework considers the artefact design and various inputs including task characteristics and organisational context as an indicator of performance. If used at an early stage of product development the framework and associated guidelines can be used to influence system design and establish how key implementation considerations impact upon user uptake and trust of the design.

The railway industry is today broadly recognised as a complex sociotechnical system that operates under considerable pressures for increased capacity and reliability. These pressures impact across the industry, in particular on rail engineering because of its responsibility in providing and maintaining the rail infrastructure. Within rail engineering, there is a growing need to address safety and operational risks emerging from high complexity. Planning has been identified as a fundamental organisational function for the safety and efficiency of engineering work. Within this scope, this thesis recognises in the planning of rail engineering work the characteristics of complex sociotechnical systems and investigates planning activities as a part of a wider rail engineering system. Resilience engineering has been recently proposed as a safety management approach that focuses on the development of means for better coping with the variability and uncertainty inherent to large scale complex sociotechnical system. The research documented in this thesis proposes the use of a resilience engineering based approach as a way to improve the ability of the rail engineering planning system to successfully contribute to the safety and efficiency of engineering work. Overall, the purpose of this research was to describe and understand human and organisational factors of rail engineering planning, understand planning performance in view of the support it provides to work delivery, and investigate improvement to the planning system based on resilience engineering concepts. A contribution to the development of resilience engineering as a discipline was also made, mainly through the investigation of possible methods for measuring and monitoring system resilience. The thesis has taken a research approach with emphasis on extensive top-down and cross-organisational exploratory work of the engineering work planning process. This was achieved through the use of quantitative and qualitative methods, namely the analysis of archival data on operational and safety performance, interviews, observations, and a questionnaire. The integration of the researcher within Network Rail’s Ergonomics National Specialist Team (NST) was fundamental for the access to a wide range of data and for the employment of a participant observation approach. The engineering work planning system is described as a complex decision making process, ranging from high level strategic business decisions down to the definition and scheduling of work delivery details. The main human and organisational factors that either hindered or facilitated planning decision making were identified and archival data were used to study planning performance. Results from these research steps were then used to support the understanding and measurement of resilience in planning. Data were interpreted in view of the resilience literature and used as basis for the investigation of potential measurement tools and system interactions with relevance for the understanding of resilience as an emergent system property. The methods used permitted a detailed description of the planning process and the identification of planning performance features within the wider frame of the rail engineering system. Human, organisational and system level factors were identified, which contributed to the understanding of planning and the identification of constraints and facilitating factors on decision making processes. Throughout the duration of this project, contributions to the development of resilience engineering and its methods were made, whilst identifying sources of resilience in the planning system and contributing to the development of measurement tools by means of a questionnaire approach. The understanding of resilience in rail engineering planning was used as a support for recommendations towards the improvement of the planning function’s ability to cope with operational pressures and successfully support work delivery.

This thesis examines the effect of automation in the rail signalling environment. The level of automation in a system can be described as ranging along a continuum from manual control to fully autonomous automation and development of appropriate automation for a system is likely to enhance overall system performance. Network Rail, the company which owns, operates, and maintains the rail infrastructure in the UK, envisions increasing levels of automation in future rail systems, but prior to this research, little structured evaluation of current automation had been undertaken. The research performed for this thesis set out to examine the impact of automation on rail signalling. A rail automation model was developed to illustrate the levels of automation present in different generations of signalling system. The research focussed on one system in particular, the Automatic Routing System (ARS). The ARS has been present in modern signalling centres since the late 1980s. It uses timetable information to set routes for trains arriving on its area of control and incorporates complex algorithms to resolve conflicts between trains. Multiple methods were used to investigate current signalling automation. An understanding of the signalling domain underpinned the research, and a model was developed to illustrate the type and level of automation present in different generations of current signalling systems. Structured observations were employed to investigate differences in activity between individual signallers. As a part of this study, a relationship was found between observed intervention levels and some of the trust dimensions identified from the literature. A video archive analysis gave initial insight into some of the issues signallers had with automation, and semi-structured interviews carried out with signallers at their workstations built on these themes. The interviews investigated four areas; signallers’ opinions of ARS, system performance issues, knowledge of ARS, and interaction with ARS. Data were gathered on a wide variety of individual issues, for example on different monitoring strategies employed, interaction preferences, signallers’ understanding of the system and their ability to predict it. Data on specific issues with ARS also emerged from the interviews, for example the impact of poor programming and planning data, and the poor competence of the system, particularly during disruption. An experiment was performed to investigate the differences between different levels of automation under both normal and disrupted running. The experiment gathered quantitative data on the effect of different levels of automation on workload and performance in addition to eye tracking data which were used to gain insight into signaller monitoring strategies. The results indicate that ARS does reduce workload and increase performance, and it does so in spite of deficiencies in terms of feedback to the signaller. This lack of feedback makes it difficult for the signaller to understand and predict the automation and, hence, creates difficulties for the operator. In addition, the methods for controlling ARS are limited and it can be difficult for the signallers to work cooperatively with the system. Principles of good automation were identified from the literature and recommendations based on these and the findings of the research were developed for future signalling automation systems. These highlighted the importance of improving feedback from ARS and the ability of the signaller to direct the system. It is anticipated that these improvements would allow the signaller and the automation to work more closely together in order to maximise overall system performance. The principles of automation are intended as a generic guidance tool and their application is not confined to rail signalling. There may also be wider implications from the research such as the influence of operators’ ability to understand and predict automation in automation use, and the existence of different types of monitoring behaviour.

Discrete element modelling has been used to capture the essential mechanical features of railway ballast and gain a better understanding of the mechanical behaviour and mechanisms of degradation under monotonic and cyclic loading. A simple procedure has been developed to generate clumps which resemble real ballast particles. The influence of clump shape on the heterogeneous stresses within an aggregate was investigated in box test simulations. More angular clumps lead to greater homogeneity and the interlocking provides a much more realistic load-deformation response. A simple two-ball clump was used with two additional small balls (asperities) bonded at the surface, to represent a single particle; it is shown that particle abrasion gives the correct settlement response. A clump formed from ten balls in a tetrahedral shape was used in monotonic and cyclic triaxial test simulations and found to produce the correct response. The interlocking and breaking of very small asperities which find their way into the voids and carry no load was modelled using weak parallel bonds. The interlocking and fracture of larger asperities was modelled by bonding eight small balls to the ten-ball clump. Monotonic tests were performed on triaxial samples under different confining pressures and the results compared with existing experimental data. Tests were also simulated using uncrushable clumps to highlight the important role of asperity abrasion. Cyclic triaxial tests were then simulated on the same aggregates under a range of stress conditions and the results compared to existing experimental data for the same simulated ballast. The clumps are able to capture the behaviour of ballast under different conditions, and asperity abrasion plays an important role in governing strength and volumetric strain under monotonic loading, and on permanent strains under cyclic loading. The contribution of this thesis is therefore to show that it is possible to model a real granular material under static and cyclic conditions, providing much micro mechanical insight.

Track deterioration has a serious influence on the safety and efficiency (speed restriction) of train operations. Many expensive, disruptive and frequent repair operations are often required to maintain the ballast characteristics due to the problem of settlement. Because of this, a geogrid solution that has proved to be a simple and economical method of reinforcing track ballast is widely used. This project presents an evaluation of the behaviour of geogrid-reinforced railway ballast. Experimental large box pull-out tests were conducted to examine the key parameters influencing the interaction between ballast and the geogrid. The experimental results demonstrated that the triaxial geogrid with triangular apertures outperforms the biaxial geogrid with square apertures and the geogrid aperture size is more influential than rib profile and junction profile. The discrete element method (DEM) has then been used to model the interaction between ballast and geogrid by simulating large box pull-out tests and comparing with experimental results. The DEM simulation results have been shown to provide good predictions of the pull-out resistance and reveal the distribution of contact forces in the geogrid-reinforced ballast system. The discrete element method has also been used to simulate cyclic loading of geogrid-reinforced ballast under confined and unconfined conditions. For the confined condition, box tests have been simulated on unreinforced samples and reinforced samples with different geogrid positions and geogrid apertures. The response of the ballast layer reinforced with geogrid under repeated loading agrees with experimental results. It was found that the optimum location of geogrid is 100 mm depth from base, and the triaxial geogrid outperforms biaxial geogrid. For the unconfined condition, cyclic loading of a trough of ballast has also been simulated, and the sample with the geogrid at 50mm from the sub-ballast layer performs best. It was also found that the used of two geogrids at both 50mm and 150mm from the sub-ballast gave a smaller settlement than using a single layer geogrid, or the unreinforced ballast. The geogrid reinforcement limits the lateral displacement in reinforced zone, which is approximately 50mm above and below the geogrid. Previous investigations have shown that the abrupt stiffness change in track support is often associated with accelerated rates of deterioration of track geometry, high maintenance demand, and poor ride quality. However, at present, there is no detailed understanding of the mechanisms of track geometry deterioration at transition zones. This work provides insight into the factors that can cause or accelerate track degradation at the transition zones, in order to identify and evaluate appropriate mitigation design. A simple track transition model with dimensions 2.1m x 0.3m x 0.45m was simulated by using PFC3D. In order to identify and evaluate appropriate mitigation methods, two kinds of transition patterns, including a single step change and a multi step-by-step change for subgrade stiffness distribution were tested. The influence of the train direction of travel and speed on the transition were also investigated. In addition, geogrid was used in the ballast layer to examine the effects of geogrid reinforcement.