Rail Industry Focus

01.11.12

Identifying earthworks risk

Source: Rail Technology Magazine October/November 2012

Julian Harms, route asset manager and geotechnical engineer for Network Rail on earthworks, discusses recent severe weather and the industry’s response.

Following a season of rain and storms, it is ever more important that Network Rail acts to adequately prepare and maintain its assets across the railway, and tries to reduce the impact of severe weather on passengers.

And this could be a phenomenon which is becoming increasingly common – with more than 30 extreme asset failures this year, compared to fewer than five the year before.

RTM spoke to Network Rail’s route asset manager and geotechnical engineer Julian Harms about the types of damage such weather could inflict, and how the company was working to improve its risk predictions and respond effectively to high-level hazards.

Extreme hazards

In response to the wet and windy months the railway has undergone this summer, Harms said: “There is no question that extreme types of weather event appear to be becoming more prevalent.

“This year has been exceptional. In the past five months we’ve had extreme rainfall events that have caused asset failures in each of those months, in some cases multiple asset failures.”

Monitoring is in place around the network to ensure the team has advance notice of movement occurring, and can respond with an intervention plan as soon as possible.

Despite having one of the “best and most comprehensive tools anywhere”, Harms admitted that it was still not picking up on high-risk locations “as well as it could do”.

This summer, a number of the locations that failed in the North West were either ‘serviceable’ or ‘marginal’, according to the hazard rating. Network Rail is therefore looking into different ways to analyse its data and identify factors unique to failure sites, to ensure a reliable indicator for risk. He commented: “That’s not something the system the currently does very well, and we are applying ourselves to do.”

Studies are ongoing in this area, as well as work on interventions to reduce the risk to the travelling public and members of rail staff. These could include using proving engines to check key lines following extreme weather, and setting thresholds for what exactly constitutes ‘extreme’ weather before triggering an intervention.

As a last resort, imposing speed limits can reduce the speed at which a train would encounter a landslip, were one to occur, Harms said.

However, this response is unpopular due to its effect on performance and customer satisfaction.

He added that Network Rail could begin to make more use of its helicopters to scout for incidents and locations where water is accumulating to highlight areas of risk.

Categorising concern

Harms said: “The damage that has been caused falls into a number of categories. The issues which cause us the most concern in the short term are the failures which affect cutting slopes.”

The two main failure types that cause such concern are earthflow failures – where soils in the cutting slope turn to a liquid state and flow onto the slope, bringing debris and boulders with them onto the track – and wash-out, where surface water erodes down into the cutting slope and brings loose material onto the track.

“The distinction is that a wash-out failure is typically due to material flowing over ground and earthflow is typically as a consequence of ground water building up within the cutting slope and finally reaching a level where it turns the material on the slope to liquid and that flows onto the track,” he explained.

Extreme weather events this summer, such as excessive rainfall, led to groundwater topping up too quickly, leading to earthflow-type failures on the Cumbrian coast.

Network Rail is currently funded to maintain its assets’ condition, where around 2% fall into the ‘poor’ condition, 48% in a ‘marginal’ state, and approximately 50% that are ‘serviceable’.

The commitment with the regulator is to broadly maintain the number of assets in each category.

Harms said: “Weathering affects it; the condition of the asset is gradually worsening all the time. We’re trying to bring it back up to an as-new condition or a well-serviced condition.”

Hazard and risk

Network Rail currently manages earthworks through an annual examination programme which scores each earthwork on criteria such as height, angle, composition, extent of burrowing, degree of vegetation cover and likelihood of water being concentrated.

This data is run through a calculation to identify the condition of the slope, or the hazard it presents of failing. Then other factors, such as proximity to the railway, line speed, complexity of layout and the level of consequences if an incident were to occur are put into an earthworks prioritisation model, which determines the areas to be prioritised for treatment and management.

Harms explained: “The hazard remains the same if it has the same features, but the risk is clearly far less if it’s nowhere near the railway.”

Earthworks are generally sorted into four categories on intervention; an emergency situation which requires an immediate response to failure, a hazard that presents a high risk but which can be monitored, a longer-scale monitored response and finally the background remedial works to maintain asset condition. The time taken to develop and apply solutions to such hazards range from one week interventions to two years of monitoring through topographic surveys, inclinometers and ground models.

Scottish signatures

Discussing interesting developments in remote condition monitoring, Harms highlighted a trial in Scotland which is seeking to identify vibration patterns associated with boulders falling, in order to warn the railway of a hazard or incident.

The trial is an updated version of a system that used trip-wires to set signals to ‘danger’ if activated.

The new listening cables are made up of fibreoptics which feedback a standard interference pattern, that changes if significant vibration – such as that caused by a rolling boulder – is picked up in its vicinity.

Harms said: “The intention is to try to pick up the signature of a boulder rolling down the slope or hillside, and that technology could be very effective. We are watching with interest to see what the conclusions are and ultimately what the cost of installation could be.

“Because if it is a more cost-effective way of managing the risk of failure at critical locations, then we would be very interested in installing something similar, say on approach to tunnels or locations where if the train did come off, it would have a much greater consequence.”

Tell us what you think – have your say below or email us directly at opinion@railtechnologymagazine.com

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