Whole-life Cost Assessment of Novel Material Railway Drainage Systems

Lead Research Organisation: University of Nottingham
Department Name: Faculty of Engineering

Abstract

Reliable drainage solutions are critical for ensuring the long-term and cost-effective provision of railway infrastructure. Water plays a significant role in the degradation of railway infrastructure and can cause poor track geometry and accelerated deterioration of ballast, with high associated maintenance and repair costs which inevitably get passed on to the end-user. Excessive amounts of water may also cause catastrophic failure of railway infrastructure systems, which represent a real threat to public safety.

Climate change is predicted to result in more extreme weather and flash flood events. The railway drainage systems will therefore be put under severe strain with increased likelihood of disruption to rail services. Much of the UK railway drainage infrastructure is old and in need of repair or replacement. However, the UK railway industry is experiencing significant growth in the number of passengers and the amount of freight carried, which reduces the opportunities available to carry out maintenance.

In light of these issues, railway drainage system modernisation is considered to be a key factor for improving railway network safety and capacity, and ensuring the infrastructure's resilience to changing weather and climate events.

This project focuses on providing novel and easily installed railway drainage solutions which make use of lightweight and cost-effective 'new materials'. 'New materials' includes those recently developed as well as materials that can be newly applied within drainage systems. The project will consider a range of materials for use in this application, such as Expanded Polystyrene (EPS) which is a lightweight and strong material with good chemical resistance. The project includes a range of experimental testing, including trials of a new material drainage system within a full-scale railway track model, as well as advanced small-scale physical modelling using the University of Nottingham geotechnical centrifuge. Numerical models will also be developed to gain a better understanding of the effects of key parameters within the drainage system.

An important component of the project is the development of tools which will allow for the assessment of the full lifecycle costs of the developed new material drainage solutions. These tools have the potential to help railway operators make informed decisions relating to the selection of track and drainage system maintenance and repair solutions. Advanced tools will also be developed which will provide a better understanding of the inter-relationships between railway drainage performance and other railway systems, including other infrastructure assets and operation services.

The project benefits from the involvement of experts from railway industry, including URS, a leading provider of engineering, construction and technical services within the railway sector, and ASPIN, who provide a range of consultancy services to the railway industry. The project will also benefit from access to information from Network Rail, the owner of the UK railway infrastructure, through proven links between the research team and representatives from Network Rail. The project fosters a multi-disciplinary approach to developing engineering solutions, with expertise from several technical areas, including geotechnics, transportation infrastructure design and performance as well as asset management.

The successful completion of the project will allow the development of modern railway drainage solutions which incorporate new lightweight, easy to install, and cost-effective materials. The lifecycle cost assessment tools developed as part of this project will enable railway operators to make informed decisions about railway maintenance and repair, and ensure that end-uses of the railway get the best service possible.

Planned Impact

The work carried out in the project will be of significant benefit to wider society, policy makers and industry. The impact of the research project encompasses a wide range of economical, societal, and developmental benefits.

The societal and economic impacts of the project are long-term, and have potential influence at both national and international levels. Effective drainage systems within railway infrastructure are essential for ensuring public safety and the reliability of the railway network, particularly when faced with future challenges from climate change and population growth. Poor drainage leads to increased rates of trackbed degradation with associated maintenance costs, and can also result in catastrophic failure of railway infrastructure which poses a serious risk to public health. A safe and resilient railway is therefore of prime importance for the economy as well as safety and quality of life in the UK. The outcomes of this project will ensure that resilient railway drainage systems can be developed using the most cost-effective options available. High-performing infrastructure is also an essential component of the UK's competitiveness in the international economic market. Solutions developed as part of this project could be marketed globally, with a clear advantage available to UK enterprise.

It is envisaged that findings, methods, and techniques developed during the project will also assist both policy makers (e.g. Department of Transport and RSSB) and practitioners in the railway industry. Project outcomes will provide guidance on the utilisation of new materials and the design and long term management of railway drainage systems. Tools developed within the project will provide new ways of assessing drainage systems in terms of interactions with other parts of infrastructure. Use of these tools will provide policy makers and practitioners with quantitative methods of evaluating whole-life costs of railway drainage assets as well as how their performance impacts the wider railway system. This will ensure that informed decisions form future policy, standards and regulations that affect railway assets.

The tools provided by the research project for the design and management of new drainage systems will offer solutions for the potential reduction of whole life costs. For example, Network Rail, the owner of the UK railway infrastructure, using the solutions offered by this project, may be able to make cost savings resulting in direct economic benefits. Furthermore, resulting improvement in the reliability of the railway infrastructure will also improve customer satisfaction, which has long-reaching societal and economic benefits since potential businesses will be able to rely on an efficient transport system.

Outcomes of the research will impact on other sectors of transportation engineering. Companies specialising in drainage solutions applicable to other infrastructure (e.g. roads) may benefit by adopting the proposed solutions.

The project also represents an opportunity to develop expertise of young professionals within a significant sector of transportation engineering and to expose them to the importance of a multi-disciplinary approach to developing advanced engineering solutions. The new skills and knowledge acquired by the early career researchers involved in this project will have significant benefit for their career development and employability.

In the long-term, the expertise gained by the project team can be successfully exploited for further developments in a range of civil engineering and operational research disciplines.
 
Description The importance of resilient infrastructure, including railway tracks, is paramount when considering predictions of extreme weather and flash flood events in the coming years. One of the main causes of instability of railway tracks is excess water in the trackbed, mainly at the interface of the ballast and subgrade. Track drainage systems should therefore have sufficient capacity to allow water to dissipate quickly, but they should also be designed to ensure long-term operation with minimal (or easily performed) maintenance. Conventional drainage systems are often susceptible to clogging and deterioration. This project provided results from an investigation of a potential new railway drainage system using geocellular components. In the project, a large scale physical model was developed which represents a full scale unit cell of a sleeper-to-sleeper track substructure. The physical model includes ballast and subgrade layers, under-track and lateral drainage systems, rainfall simulation, and instrumentation. Results demonstrate the relative hydraulic response of the drainage system with and without including the geocellular components. The project also developed a numerical model of the drainage system, which was first calibrated and verified using experimental data, then extended to study the effect of various other parameters on the hydraulic response of railway track. Results indicate that the under-track geocellular drainage system offers potential benefits in terms of maintaining a lower water table level within the subgrade as well as for aiding the migration of fines out of the ballast.

From an asset management perspective, the overall contribution of the project is a novel railway drainage asset management framework, which is customised for the physical reality of the asset (e.g. lack of data, uncertainty in geomechanical and hydraulic parameters). This framework is based on a hybrid model-data approach whereby physics-based models and degradation data are combined in a coherent probabilistic sense.
Exploitation Route Further testing and analysis should be conducted prior to implementation, in particular an evaluation of the mechanical response of the drainage systems within a ballast system and the modelling of the dynamic response of the ballast to train loading. From an asset management perspective, the main contribution is a generic methodology for railway drainage asset management; this methodology can be widely used by modellers and researchers for further developments.
Sectors Construction,Transport
 
Description Dean of Engineering Scholarship
Amount £60,000 (GBP)
Organisation University of Nottingham 
Sector Academic/University
Country United Kingdom
Start 07/2017 
End 06/2020
 
Title Analytical model for steady state water flow in sloping layered porous media 
Description A new steady state model for water flow in layered porous media has been developed based on the Dupuit-Forchheimer theory. The model predicts the water table elevation for unconfined sloping systems with an unlimited number of non-parallel layers, where recharge is drained to a downstream boundary. 
Type Of Material Computer model/algorithm 
Provided To Others? No  
Impact The model developed for water table height is shown to generalize the one proposed in E. Youngs, K. Rushton, "Steady state ditch drainage of two-layered soil regions overlying and inverted v-shaped impermeable bed with examples of the drainage of ballast beneath raiway tracks", Journal of Hydrology 337 (3) 2009 pp 367/376, for two parallel layers so that it becomes a particular case of the model proposed. This generalization for more than 2 layers including non-parallel layers is crucial when considering the railway internal drainage under real service conditions, since maintenance activities like ballast tamping or degradations processes like the ballast fouling actually lead to additional non-parallel layers that greatly modify the hydraulic behaviour of the system. In addition, the adoption of an analytical model instead of numerical models like Finite-Differences is key for life-cycle assessment, where thousands of models evaluations are required. 
 
Title Bayesian inverse problem algorithm to assess model accuracy 
Description A full Bayesian inverse problem framework has been developed to formally assess the suitability of the proposed analytical model for water flow for the many possible values of model parameters. To this end, the performance of the proposed model is probabilistically compared against a reference numerical model using MODFLOW-NWT, the open-source FD code by the U.S. Geological Survey for unconfined groundwater flow. 
Type Of Material Computer model/algorithm 
Provided To Others? No  
Impact Within the proposed Bayesian framework, the assessment is systematically carried out through relative probabilities that measure the degree of belief of the uncertain hypothesis that both models, namely the proposed model and MODFLOW-NWT, render identical outputs for the different values of model parameters. It not only allows a systematic efficient comparison of the models, but also provides a rigorous framework to account for the various types of modeling uncertainties (discretization error and truncation error, among others) within the assessment. The proposed methodology is general in nature, thus, it can be extended to any other model different than the ones developed in this project. 
 
Title Full scale physical model for railway drainage system 
Description In order to study the effect of novel materials on the hydraulic response of railway drainage system, a 1g model has been designed and developed in Nottingham Centre for Geomechanics. The physical model represents a full scale unit cell of the sleeper-to-sleeper track substructure with dimensions of 4880 mm in length, 1220 mm in height, and 620 mm in width. The model is capable of accommodating subgrade and ballast layers, as well as drainage pipe on the side. More importantly, different rainfall scenarios (varied the ratio of rainfall intensity to the coefficient of permeability) can be simulated in this physical model and changes in water table level can be captured both visually (through Perspex windows) and pore water pressure transducers connected to the box. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? No  
Impact The data obtained from this developed physical model provides the effect of new drainage components to be used as part of railway track drainage system on the hydraulic response. Also, the results of water pressures from transducers can be used to calibrate a numerical model (2D and 3D). Following this calibration, the numerical model can be extended to study different parameters (including geometry and location of new drainage components) on the response of railway track drainage system to rainfall. 
 
Title Infrastructure asset management model based on Plausible Petri Nets 
Description Petri-nets (PNs) are an efficient tool to model distributed non-linear systems, like the degradation and maintenance modelling of the whole railway infrastructure. However, they have a well-known limitation when dealing with continuous uncertain variables (like the degradation of the track). A new type of Petri-net formalism has been developed to deal with uncertain variables, which combines PNs principles with the foundations of information theory. The resulting framework has been named Plausible Petri nets (PPNs). The main feature of PPNs resides in their efficiency to jointly consider the evolution of a discrete event system together with uncertain information about the system degradation state using plausible states of information. 
Type Of Material Computer model/algorithm 
Year Produced 2017 
Provided To Others? Yes  
Impact PPNs are shown to act as a hybrid expert system combining symbolic discrete items (e.g., go/no-go decisions, resource availability, etc.), and numerical values (e.g., degradation variables, expert opinion, etc. ) subjected to uncertainty, which allow us to make realistic simulations about the life-cycle performance of the whole infrastructure. This tool could act as a computational "virtual twin" of the infrastructure, which would allow an optimal asset management and anticipated decision making. 
 
Title Prognostics-based drainage asset management model 
Description A particle-filter based prognostics approach has been developed which integrates the physics of the drainage degradation (ballast degradation, flow in porous media, and rainfall simulation) and experimental data (water pressure, settlement) within a rigorous probability-based framework that allows predictions of the time to reach a functional limit with quantified uncertainty. This physics-based prognostics framework is subsequently embedded into an asset management model based on Petri nets, which allows the consideration of management activities into the overall system predictions. 
Type Of Material Computer model/algorithm 
Provided To Others? No  
Impact Predictive information about drainage performance can be a valuable resource in determining an appropriate course of action to avoid system failures. Potential of prognostics in positively contributing to safety and improving life-cycle costs of the railways is equally relevant to existing legacy systems and new system designs. Legacy systems adopt additional sensing and processing with a potentially high price of retrofitting and additional validation and/or certification costs to gain extended system life and safety factor. New system designs like the one proposed in this research for railway drainage can significantly reduce these costs if physics-based prognostics and condition monitoring are adopted early in the design to facilitate a more optimal asset management. This, however, it requires integration of condition monitoring and the modelling of the system behaviour into the asset management process. The prognostics-based asset management methodology developed allows for such integration in a soundly and rigorous way. 
 
Title Recording the variation of water level in field trial along with weather condition 
Description In order to monitor the water table variation over time under both seasonal changes and track loading, pore water pressure transducers and weather station have been installed at field trial. It is located in Midland Railway Butterley, Ripley. The transducers were installed at different location along the railway track to cover sections both relatively good and bad conditions in terms of track drainage. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact The results of this data collection will be used in the following areas: 1- Assessing the current condition of a railway track drainage and then, once the new solution is proposed it can be compared to show the effectiveness of the new drainage solution. 2- Calibration of the hydraulic numerical model 3- The results of the analytical model can be compared with the real data collected. 
 
Description Supervision of an industrially-based PhD student 
Organisation AECOM Technology Corporation
Country United States 
Sector Private 
PI Contribution PhD supervision + associated outputs
Collaborator Contribution Employment of student; Data provision; General collaborative information sharing
Impact None so far
Start Year 2017
 
Description Article in Rail Technology Magazine 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Article published in magazine which gives an overview of the research project. I had several people from industry contact me about the work as a result.
Year(s) Of Engagement Activity 2015
URL http://www.railtechnologymagazine.com/Comment/university-of-nottingham-researchers-investigate-use-o...