Stability of railway cuttings must be monitored more closely to avoid a repeat of a landslip last Friday which derailed a train near Watford, a technology specialist has said.

Two lines were shut over the weekend after the 6.19am service from Milton Keynes to Euston left the track outside a tunnel and was clipped by a second train heading north at the same moment.

“More needs to be done to monitor the structural health of railway assets and infrastructure,” said Dr Mark Brown of geospatial technology firm 3D Laser Mapping. “Weather is getting more extreme and an increased number of incidents like this could easily happen.”

Dr Brown added that constant monitoring can identify at risk areas, provide early warnings and predict events before they cause major damage. He went on to say that the French rail operator SNCF monitors over 29,000km of its track using mobile mapping technology and the UK rail industry should do the same.

Network Rail head of geotechnics Simon Abbott said: “Earthworks across the rail network are principally monitored by walkover inspections and aided by the use of drones, helicopters and maintenance trains. We also use video, LIDAR and aerial photography to assist in the identification of areas at risk and put in place more rigorous monitoring where necessary.”

This latest incident is not the first time this year railway lines have been blocked following a landslide. In January a bank slip near Leighton Buzzard closed the West Coast Mainline and the following month the Settle to Carlisle route was closed after high rainfall had saturated nearby ground.

Network Rail route managing director Martin Frobisher said that its engineers spent the weekend outside the tunnel near Watford clearing slip debris, removing the damaged trains, replacing 50 concrete sleepers and welding new sections of track.

Ground engineering specialist Dr Fleur Loveridge of the University of Leeds' school of civil engineering said the cause of the Watford incident is likely to be a combination of factors.

“Photographs of the landslip appear to show that work had been done on the steep chalk cuttings on the approach to the tunnel. This may have included removal of vegetation and the installation of catch netting.

“From this information it is not possible to know whether removal of the vegetation was the cause of the slip. But while trees on steep chalk cuttings are themselves a major hazard to the railway, it is also the case that taking away vegetation does remove support from the near surface material.”

Dr Loveridge added that the condition of the Network Rail and / or third party drainage at the top of the slope is likely to have been a significant factor given the very intense rainfall in the area last week.

A spokesman for the Institution of Civil Engineers commented: “It is not clear what set off the landslip at Watford. There had been torrential rain which is likely to have been a contributory factor but it will be interesting to hear the outcome of the investigation to find out the exact cause and see what lessons can be learned.”

He noted that many of Network Rail's embankments and cuttings were built before there was a proper understanding of geotechnical engineering, and said that to prevent all landslips is not possible without incurring “unacceptable” costs.

This combined with the fact there is an increasing likelihood of severe rainfall due to climate change means “Network Rail needs to monitor its structures on a regular basis”, the spokesperson added.

A spokesman for Network Rail said: “Torrential downpours overnight appear to have caused a flash flood which washed the embankment onto the railway below.

“Ongoing maintenance work has seen planned vegetation removal at this location to help stabilise the embankment, along with netting to make it even safer. Contrary to popular belief, trees on steep embankments can actually cause or make landslips even worse.

“A full investigation into this incident will take place to establish the facts.”

(Photo: Network Rail)