Case study: Value-based tunnel repair strategy
Background
Railway tunnels are reliable structures with relatively low maintenance requirements; but some problems do occur which can be challenging to fix. Ground water seepage is the most common concern in many railway systems. This can be a particular issue in older tunnels not built to modern waterproofing standards.
Uncontrolled seepage can result in a variety of condition problems including: corrosion of track and structures, disruption to signalling and other electrical systems and general deterioration of surfaces. If untreated, these issues can lead to reliability issues and a poor ambiance in public areas.
The precise location of seepages can be hard to predict so maintenance to correct specific instances is often reactive in nature. This can make effective maintenance planning difficult.
This case study examined such a situation in London Underground (LU) tunnels where seepages have occurred. London Underground carries approximately 1.2 billion passengers per year, and London's contribution to the national economy significantly depends on the delivery of that capacity. With parts of the tunnel network now more than 150 years old, maintenance is essential to realise value from the infrastructure.
The organization has invested in trials of materials and methods to treat these issues. These have established a palette of remedial solutions together with published guidance on the design and implementation of grouting to control individual seepages. The logical next step was to develop a strategy to select a treatment approach taking account of what the railway values in different locations. For example, the right treatment for a running tunnel may not be same as for a public area where appearance is important.
Project objectives
The key objective is to determine the best repair option for seepage problem occurring in tunnels. In doing so, ensure that the repair option achieves the best value for money and has least business impact. The context of the problem was to determine the repair option for a specific seepage in any particular tunnel within the portfolio. This will allow in determining the variations of the repair options depending on tunnel's location and its criticality to the network. Therefore, this would allow London Underground to develop intervention options depending on the tunnel and its criticality, thereby develop a strategy for the portfolio of tunnels.
Approach
We used the value-based approach to determine the stakeholders of the underground tunnel (e.g., LU operations, LU maintenance, customers, Mayor of London, employees), and their requirements. Further the requirements of the different stakeholders were translated into a number of measurable value drivers and associated metrics. A value map was then developed - this showed how different deterioration and failure modes of the tunnels could directly or indirectly (through interactions with other assets in the tunnel, e.g., signalling system and tracks) affect the value drivers. This value map was then translated into a mathematical optimisation model that considered a 50 year horizon to find the optimal repair option for a given location in the underground tunnel network.
Benefits
- Cost saving by making informed choices on the type and timing of repair striking the right value vs cost balance.
- Minimise disruption to the London Underground service by structured identification and minimisation of risks
- Enhancing value to the organisation by providing a standard systematic approach for making asset management decisions
