Landslips can follow heavy rain – like in the North West of England today.
Flooding has caused one of these incidents in Dent in Cumbria, affecting trains between Carlisle and Leeds.
What is a landslip?
Landslips happen on the railway when soil, rocks and earth fall on to and cover the track. This is often after long periods of heavy rain, when the ground becomes saturated with water.
Landslips can cause a lot of disruption and delays on the railway by obscuring the track. A train can’t swerve to avoid debris on the line, so we will often need to re-route services.
Our specialist geotechnical engineers work across Britain to stabilise and repair weakened assets, enabling a network more resilient to future risk events, such as extreme weather.
What we do when there’s a landslip
Following an emergency like this, we deploy our engineers to carry out any immediate works to the affected areas; some of our previous weather-related emergency repair works includes stabilising hillsides and repairing cutting slopes.
Even after an initial landslip there continue to be concerns, so our engineers and contractors will assess the site and the damage before they can start to remove the debris from the track. Once a landslip has started to move, it’s much more likely that there will be further landslips.
Some of the slopes – or cuttings – on either side of our tracks need to be strengthened. This work to stabilise the earth can take time.
On 12 February, a landslip in South East London led to a line closure to make the railway safe again for passengers. Our engineers responded in the early hours to the situation in Barnehurst, where ground conditions are unusual for London:
At Barnehurst, the landslip occurred on a cutting – where the railway is lower than the ground, as opposed to an embankment, where the railway is raised above the ground.
The geology of the ground here is referred to as Harwich formation, which means there are lots of layers of silt, gravel and clay.
Any rain that falls percolates down and when it hits the clay layer, the water can’t go any further, resulting in the saturated soil and a landslip.
These types of ground conditions are quite unusual for London, where clay or chalk are typical.
In this case, we were alerted at 4am and implemented a safety speed restriction. One of our engineers visited the site and decided it was unsafe to run trains through the cutting.
Once the landslip had stopped moving, the site was safe for us starting work immediately, beginning with the clearance of any slipped or unstable trees.
We decided to make the cutting safe by using H piling, where we drill holes into the earthworks and insert H-shaped steel beams into the ground to essentially build a wall that will prevent slippage.
Carrying out the work safely requires a line closure but this means we can fix the problem relatively quickly.
How we’re reducing delays caused by landslips
- It’s important we identify the sites prone to landslips to ensure we keep passengers and our engineers safe. We use helicopters equipped with laser imaging, detection and ranging to do this.
- Where we know sites are at risk of landslip, we use motion sensors and CCTV to detect soil and rock movement. These sensors send an alarm to the signaller, who will stop the train if alerted and wait until the area has been inspected by engineers.
- We can also stabilise the slope by putting in drainage or using steel rods or soil nails.
- If these options are insufficient, we will re-profile the slope to reduce its angle, making it less prone to a landslip.
- When we get flood warnings from the Environment Agency and Flood Forecasting Centre, we send people and equipment to the at-risk areas so we’re in a position to act quickly.