photo: Santanu Sen / Flickr/Illustrative photo
South Western Railway will introduce a temporary timetable between London and Exeter from 10 August. The reason is not damaged trains or a signalling failure. The ground beneath the railway is shrinking.
Long periods of heat and low rainfall have dried out the clay embankments that support the West of England Line. As the clay loses water, it contracts. Sleepers can then move sideways or drop, which changes the position of the rails, consequently making normal speeds unsafe. Trains must slow down until engineers can stabilise the track.
The problem is already affecting the timetable. Services between Yeovil Junction and Exeter St Davids will run once every two hours. Journeys between London Waterloo and Exeter may take 24 minutes longer in one direction and 27 minutes longer in the other.
Why Clay Embankments Shrink in Dry Weather
Many older British railway embankments contain clay, which holds a large amount of water under normal conditions. Heat, drought and nearby vegetation gradually remove that moisture. The clay then loses volume, leaving gaps beneath sleepers or causing sections of the embankment to settle unevenly.
South Western Railway calls the process Soil Moisture Deficit, or SMD. The operator says the problem is especially serious on the route between Salisbury and Exeter, as this section is mostly single-track and has only a limited number of places where trains can pass each other. A speed restriction on one section can therefore delay services across a much larger part of the line.
The earthworks themselves are also part of the problem. Many were built long before engineers had modern knowledge of soil mechanics, drainage and long-term climate risk. University of Southampton research notes that railway embankments often contain clay that shrinks in summer and swells again during wetter periods. Repeated movement can gradually weaken the earthwork and disturb the track above it.
According to Lawrence Bowman, the managing director of SWR and Network Rail Wessex, this is the second consecutive summer in which dry ground has forced timetable changes on the West of England Line. The temporary timetable introduced in 2025 remained in place until November.
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Why More Ballast Is Not a Permanent Solution
The quickest response is usually to correct the track with a tamping machine. The machine lifts the rails and sleepers, then pushes ballast beneath them to restore the correct level. According to The Guardian, Network Rail treated around 100 kilometres of track on routes in eastern England in 2025. It also expects to use 49,000 tonnes of ballast during 2026 as dry conditions continue to affect the network.
SWR and Network Rail Wessex have carried out similar work between Salisbury and Exeter. Since last summer, they have monitored more than 30 vulnerable sites, installed thousands of tonnes of new ballast and removed trees that were drawing moisture from the embankments.
But ballast only corrects the track position. It does not stop the clay below from shrinking. SWR says tamping may soon be undone if engineers carry out the work while the ground is still moving. The soil first needs to regain enough moisture, which might require weeks or even months of rain. Until then, engineers may have to keep the speed restrictions in place.
Bio-Cement, Foam and Sleepers That Adjust Themselves
SWR and Network Rail Wessex are now working with the University of Southampton’s National Infrastructure Laboratory on longer-term options, among which are:
- Bio-cementation, which would inject nutrients into the soil below the track. This encourages the formation of a calcium carbonate structure, which could provide extra support when the surrounding clay contracts.
- Injection grouting, which would fill gaps with expanding polymer foam. The foam could strengthen the track formation and reduce movement caused by shrinking soil.
- Self-adjusting sleepers, which would contain a reserve of small stones. If a void opened beneath the sleeper, those stones would drop into the space and help keep the track level.
- Micro-piling, which would add small supporting piles between the rails. These would stiffen the ground below the track and limit movement during dry periods.
The operator has not yet presented these methods as a finished solution. They are options being researched and tested. Each one would also need to work on an operational railway, where construction access is limited, and trains continue to place heavy loads on the track.
Heat Is Changing Rail Maintenance Across Europe
The West of England Line is one local example of a much larger problem.
A 2026 assessment by the European Union Agency for Railways drew on data from 23 infrastructure managers covering almost 80% of the EU network. It found that flooding, landslides and windstorms caused the greatest disruption, while heatwaves and wildfires were also becoming more serious. ERA has called for climate projections to be taken into account when European standards for embankments, bridges, drainage and other infrastructure are reviewed.
Reuters reported that more than 70% of European rail infrastructure managers are seeing growing disruption from extreme weather. Operators are responding with a mixture of established engineering and newer technology. This includes drones for inspections, AI-supported sensors, more stable sleeper designs and closer monitoring of vulnerable infrastructure.
Some solutions are much simpler. Stockholm’s transport authority has painted sections of metro rail white to reduce heat absorption and lower the risk of track buckling. Britain’s Network Rail has prepared regional climate adaptation plans for the 2024–2029 funding period.
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Could the Same Problem Affect Central Europe?
Shrinking clay is not a uniquely British process. Clay-rich earthworks can lose volume when they dry and expand again when water returns. That does not mean every Central European railway faces the same level of risk as the line to Exeter. The effect depends on the soil, the way the embankment was built, drainage, vegetation and the local pattern of rainfall and heat.
However, ERA’s findings show that climate resilience is already a European infrastructure issue rather than a national one. Its recommendations specifically include closer assessment of embankments and the use of future climate projections in technical standards.