By John Challen

The latest CIHT report focuses on the challenges in achieving a resilient transport network and features many case studies to show what can – and needs – to be done. One of these centred on earthwork deterioration by using work carried out by Mott MacDonald, Coffey and Winter Associates for National Highways.

A key figure in the project was Christopher Power, Engineering Geologist at Mott MacDonald. “We undertake work for National Highways, specifically around the performance of earthworks,” he explains. “The strategic road network for National Highways is held up by these earthworks, which are made out of natural geological materials and exposed to the climate.

“They particularly struggle when it rains too much and, sometimes, when a changeable climate brings repeated wetting and drying, which causes problems within maintenance, such as [the] swelling and cracking of clay embankments.” 

Power says that while the motorway network is relatively new, it’s showing signs of deterioration and, occasionally, landslide-type movements: “From a resilience point of view, it’s about understanding how the earthworks are behaving and then thinking about what a changing climate is going to those earthworks. That was the driver behind the work we've done for National Highways in this space.”

Looking to the future

Power says that he and his team drew on almost 20 years of existing asset condition data within the Geotechnical and Drainage Management Service (GDMS), the National Highways’ geotechnical asset management system. Using this data, Markov chain modelling was undertaken to extrapolate both asset condition and the estimated number of annual slope stability issues through to 2080.

“One of the key differences in this piece of work – compared with anything we’ve done before – is that we also wanted to take account of the changing climate and how earthworks might deteriorate through time because of that,” states Power. “We brought in some work from the ACHILLES university research programme, which looked at modelling the performance of earthwork slopes into the future, taking climate change into account.

“That information [showed] increased rates of deterioration, which we then brought into our work, adding some engineering knowledge and producing some climate change-adjusted deterioration curves for the future.”

The results were revealing and illustrated the size of the task at hand without intervention. “We looked at numbers around expected numbers of issues annually in, for example, embankments,” Power says. “The current number is around 100 issues a year and, in the future, there is a gradual increase in this figure as time goes on, as you might expect from an ageing asset portfolio. But when we apply accelerators for the impact the changing climate might have – based on some of the climate modelling – there are notably more issues.

“According to our work, if the climate remained the same, by 2050 National Highways would be dealing with approximately 125 embankment issues a year. However, if the climate changes as expected, which all indications suggest is likely, there could be as many as 175. Increasingly, organisations such as National Highways are having to make decisions to support the modelling and also having to run investment models to see how much money might be required [to carry out proactive maintenance and fix these issues].”

The data concludes that by 2080, the climate change-affected figure could be up to 225 embankment issues a year under a worst-case scenario. “By carrying out this advanced modelling, informed by world-leading research and expert judgement, National Highways have a handle on the scale of the potential challenge, and can prepare plans to adapt to the changing climate to ensure that they can deliver a resilience strategic road network in England” says Power.

Next steps

Download CIHT’s ‘Delivering a resilient transport network’ now.

Newsletter image: aerial view of the M62 running alongside Scammonden Reservoir, Calderdale, West Yorkshire; credit: Shut-terstock