Extending the life and capacity of Europe’s ageing tunnels and bridges

As critical infrastructure in Europe’s railway network, tunnels and bridges smooth the passage of trains over and under potential obstacles. Yet much of this infrastructure is over 50 years old and approaching its end of life. It was also designed to codes and standards no longer aligned with today’s more stringent requirements for railways and rolling stock. Moreover, tunnels and bridges will increasingly have to cope with the ever-growing demand for higher capacity in terms of availability, speed, and axle loads.

European railway passenger and freight traffic continues to rise. By 2030, passenger traffic is forecast to rise by 34% and freight by 40%, compared to a 2005 baseline. This means the access time to bridges and tunnels, for inspection and repair, will be reduced. Structures will thus deteriorate faster, due to fewer inspections being made or inspections of less quality. Delayed detection of damage will lead to longer and costlier repairs in the long run, severely impacting track availability due to extended track closures.

Inspection costs for this infrastructure could potentially be halved, through enhanced inspection methods and techniques. These would also improve the quality of inspection, while reducing the costs for corrective maintenance on the main structures, including tunnels and bridges.

Under the Shift2Rail programme, five technology demonstrators were used on proactive assessment, repair, and upgrades of both tunnels and bridges. They showed that major infrastructure improvements are feasible, by using innovative and sometimes automated solutions to monitor and repair structures. Earlier and improved detection of ongoing and potential deterioration will lead to increased security, by doing the right maintenance on the infrastructure at the right time.

Tunnel demonstrators: easier/faster inspections (and repair of) tunnel lining and drainage pipes, thus lowering maintenance costs and increasing the network’s capacity and reliability.

Bridge demonstrators: extension of the life of bridges, thanks to better fatigue assessment, plus the reduction of noise and vibrations for train passengers and nearby residents.

Tunnels

The EU network includes more than 3,000 km of tunnels over 1,000 m long. Maintaining their drainage system is a big challenge, as is the internal blockage of long tunnel drainage pipes. Engineers must also keep tunnel lining structures in good condition, by battling deterioration due to water ingress and joints, plus concrete or brick lining deteriorating and spalling. All these issues can create points of low structural resistance.

Here, the two tunnel demos developed and demonstrated innovative methods to monitor tunnel health, as well as to improve tunnel drainage and install new lining or replace defective lining:

Solution: Tunnel health demonstrators

• What: Demonstration of tunnel health monitoring.
• Work: Tunnel drainage monitoring system, tunnel health monitoring system, and tunnel structural monitoring system were all demonstrated, generally reaching TRL6/7 (technology demonstrated in a relevant environment/system prototype demonstration in an operational environment).
• Result: Development and testing of a prototype of a Tunnel Substructure Investigation Radar (TSIR) radar system, which successfully produced 3-D images of tunnel subsurface morphology. Also, tunnel structural monitoring using fibre optics, reaching a good point of maturity and TRL6 (technology demonstrated in a relevant environment).
• Who benefits: Infrastructure managers, Railway operators.

Solution: Tunnel improvement demonstrators

• What: Demonstration of tunnel improvement.
• Work: Development and testing of improvements to tunnel drainage and (new or replacement) lining.
• Result: Development and demonstration of tunnel improvements by 1) faster restoration of tunnel drainage (including long-distance flushing systems, improvement of pipe materials and repair of damaged pipes); 2) faster replacement of damaged lining with reduced traffic disturbance and better working environment (e.g. 3-D scanning and tailored manufacturing of spare parts, with perfect fit/installation at the scanned location); and 3) adaptable and tailored tunnel lining, using fibre reinforced concrete applied by a robotic shotcrete technology. Developed tunnel repair technologies generally reached up to TRL7 (system prototype demonstration in an operational environment), while repair mechanisation techniques reached a lower level.
• Who benefits: Infrastructure managers, Railway operators.

Bridges

At the last count, there were over 200,000 bridges over the EU’s railways. Many are near the end of their service life. Some were built to codes that did not take into account fatigue loading, which particularly affects bridges on high-frequency lines. To meet these challenges, hopes are being pinned on numerical simulation techniques, together with physical inspection and maintenance data. These will help to manage uncertainties and reinforce the administrative upgrading approaches and the design of future structures, e.g. new bridges to carry high-speed trains.

Under the three demos on bridges, R&D highlighted new ways to monitor bridge health, both optically and virtually, as well as to improve bridge service capability and build high-speed low-cost bridges:

Solution: Bridge health monitoring demonstrators

• What: Demonstration of bridge health monitoring.
• Work: Monitoring of the health of bridges through optical and virtual monitoring methods.
• Result: Successful demonstration of monitoring bridges health with three methods: 1) optical monitoring methods for geometry and digitalisation; 2) enhanced fatigue capability utilisation by virtual monitoring (creation of a digital twin) of critical components; and 3) scour monitoring from train-induced vibrations. All three methods reached TRL7 (system prototype demonstration in an operational environment). Partly developed: a digital twin framework for bridges and integrated fatigue consumption system. Also demonstrated: instrumentation of a Swedish bridge and a train, and monitoring of a solution for bridge fatigue consumption.
• Who benefits: Infrastructure managers

Solution: Bridge service capability improvement demonstrator

• What: Demonstration of improvements to bridge service capability.
• Work: Assessing bridge service capability, including improved bearing capacity and the fatigue capacity of railway bridges with a focus on not disturbing traffic during installation.
• Result: Successful demonstrations of 1) improved shear capacity of railway bridges (including demonstration of the shear strengthening technology developed for use on concrete trough bridges, without causing traffic disruptions) with the developed solution, on a bridge in Finland; 2) fatigue capability improvement, after evaluation of fatigue life extension of the fatigue-prone details of UK steel bridges strengthened by externally bonded FRP plates; and 3) classification capacity, including determination of the load-bearing capacity of U-frame bridges, plus a finite element model (developed and calibrated) to determine stresses generated in different bridge components. Bridge repair technologies were demonstrated to reach up to TRL7 (system prototype demonstration in an operational environment).
• Who benefits: Infrastructure managers, Railway operators.

Solution: High-speed low-cost bridges demonstrators

• What: Demonstration of a new methodology to estimate damping coefficients in railway bridges for high-speed trains.
• Work: The focus was on improving the design of bridges for high-speed trains, to increase safety and avoid unnecessary/expensive over-engineering of bridges. Researchers assessed railway bridges under rapid cyclic loading (soil-structure interaction) and railway bridges with non-ballasted tracks.
• Result: A new methodology to assess the real value of damping coefficients in railway bridges. This methodology will 1) reduce the need for over-engineering of railway bridges; 2) enable a more cost-effective approach to bridge design; 3) enable future revision of a European standard for traffic loads on bridges; 4) help train builders with the design of future high-speed trains.
• Who benefits: Infrastructure managers, Railway operators.

Main results

• Several tunnel inspection technologies were developed, offering the highest LCC (Life-Cycle Cost) and a step change in RAMS (Reliability, Availability, Maintainability & Safety). It was shown they can be used for different tunnel types and different stages of deterioration.
• The same was achieved for bridge inspection technologies, demonstrated on a selection of bridges in a full operational environment.
• Tunnel repair technologies were developed and demonstrated by small-scale testing, in the laboratory and operationally in sections of real tunnels.
• Some innovative repair techniques for bridges were demonstrated on real structures in an operational environment in the service limit state, e.g. selected strengthening methods and methods to reduce noise from metallic bridges.
• Systems for bridge monitoring over time, filtration of data and storage of information in models were partially developed and proven, thanks to virtual demonstrators using real data from laboratory tests or fictitious data from real structures.
• Newly monitored and strengthened structures were tested for increased capacity and reliability.

Conclusions

With the developed technologies (most of which reached TRL7), the Consortium reckons that expensive tunnel and bridge inspections can be reduced by 50%, while improving safety and quality. The developed methodologies are reducing inspections frequency and complexity, and repair times, making some of the key repair tasks more automated.

For tunnels, the innovations demonstrated in this project are promising and could reduce track closures for inspections by between 20 and 30%. Inspections of tunnels were demonstrated to be faster, partly automatic, and with enhanced quality. The inspections can become more objective, quantified and deterioration can be detected before defects arise; inspection results are also more repeatable. Enhanced inspection would improve planning and actions could be planned well ahead, to a lower cost with fewer traffic interruptions.

The demonstrators also showed the potential for improved drainage cleaning of old tunnels, while maintaining traffic operation, thanks to mechanisation concepts for tunnel maintenance and repair.

Inspections of bridges were demonstrated to be feasible when partly automatic, and with greater quality. The achieved inspection techniques are more objective, quantified and can help to detect deterioration before defects arise. As with tunnels, enhanced inspection would improve the planning and cost of remedial actions, with fewer delays to traffic.

For bridges, strengthening methods were demonstrated as beneficial. They can preventatively reduce future structural issues associated with structural resistance and stability, as well as fatigue response. Developed strengthening methods were also enhanced, by improving structural durability and ductility.

The research highlighted how the remaining life of existing bridges could be extended by more than 10 years on average, although this will depend on the type of bridge and maintenance status. Another positive outcome was the potential to reduce noise and vibration intensity on bridges.

New industrialised methods, as well as refined codes and standards, could help to reduce costs for bridge construction. However, more work is needed to quantify or demonstrate this, alongside further research on tunnel automated lining repair, e.g. 3-D scanning, 3-D printing, and installation.