The terms ‘global warming’ and ‘climate change’ are often used interchangeably, but they are not identical. Global warming refers specifically to the long-term rise in average temperatures, while climate change captures the broader shifts in weather patterns, rainfall, and storm events. Both have profound implications for the stability of the UK’s earthwork assets.
Recent polls in the UK suggest that the number of people who think the effects of global warming are exaggerated has risen by over 50% and public scepticism about climate change is growing. More people believe the effects of climate change are also exaggerated, which correlates with declining support for environmental policies and restrictions on petrol and diesel cars. For those of us working in geotechnical engineering, the evidence is clear and visible.
Over the past decade, GeoAccess has been supporting Network Rail in maintaining its geotechnical earthworks and has witnessed significant changes on the ground. The number of days spent on track blowing into your frozen, gloved hands and traversing slopes with sparse, wilted vegetation are fewer. Vegetation that once died back by late autumn and allowed for a compliant inspection, now often lingers long into winter, in some locations never disappearing at all.
The earthworks ‘season’ was once consistently between November and March, but in recent seasons this has extended well beyond April. We have had to adapt and are now sending an increasing number of examiners onto the network with a vegetation clearance crew from the start of the season to combat the stubborn presence of dense vegetation levels. This ensures a greater number of exams are undertaken on the first visit.
Stable systems?
A geotechnical earthwork is typically defined in Network Rails’ CIV065 standard as a slope that is three metres in height or more. They may be composed of soil, rock, or a mixture of both. They may seem static, but these slopes are dynamic, ‘breathing’ systems influenced by geology, hydrogeology, vegetation, and human intervention.
The principle of slope stability is simple: a disturbing force acts against a resisting force. When the disturbing force exceeds resistance, failure occurs. Therefore, every failure has a cause: there are no true ‘accidents’ in geotechnical terms. Typically, a slope failure may result from a loss of toe support, addition of load at the crest, or a reduction in soil strength. For rock slopes, water infiltration along pre-existing fractures is the primary trigger, weakening joints until failure occurs.
It is often considered that vegetation helps to stabilise slopes. While that may be true for certain aspects, there are conditions where this creates a new hazard. For example, a sandy loam overlying bedrock that has now been bound together into one large mass. If the equilibrium between the opposing forces is disturbed, such as following a period of wet weather or strong winds, catastrophic failure may occur resulting in the large singular mass sliding downslope onto the infrastructure. Whereas before, it may have been more susceptible to gradual soil creep or localised slumping.
Conversely, stripping all vegetation leaving an exposed slope may lead to saturation of the soil, a lowering of shear strength, and resulting in large scale failure. This is why trained and experienced geotechnical engineers are required to undertake careful evaluation of factors including slope geometry, geological composition, and existing drainage conditions when assessing the risk of failure from an earthwork.
Water is the principal driver of slope instability. We emphasise this in training, highlighting the importance of assessing the condition of existing drainage systems during inspections, and educating examiners on how changes in groundwater levels can instigate slope failure. Undertaking proactive visual inspections on site is essential to effective earthwork management: examiners must identify early warning signs of instability, evaluate drainage effectiveness, check the condition of retaining structures, and evaluate catchment areas that direct water to slopes.
There is a clear correlation between weather events and the number of reactive assessments required on the network. The MET office confirms that the UK now experiences more frequent and more intense storm seasons, peaking between October and March. The winter of 2023-2024 was one of the wettest on record with rainfall around 20% above normal and one of the most active storm seasons ever logged. This is correlated with a peak in winter callouts onto the Network to undertake our reactive assessments over the same period. We are expected to surpass 500 requests to attend reported failures this coming winter and have regularly experienced a surge in demand when a named storm is rolling across the country during this time.
Proactive not reactive
These trends highlight both the importance of proactive slope management and the impact that excess water levels have on earthworks. Geotechnical inspections that identify where early intervention is required are cost-effective in the long term and protect critical infrastructure. Allowing earthworks to repeatedly fail on your infrastructure before reacting is not sustainable, this results in a larger financial and reputational cost.
GeoAccess is uniquely positioned to support infrastructure owners in safeguarding geotechnical assets. Our team of experienced geotechnical engineers can categorise earthwork slopes, assign risk ratings, and conduct thorough site inspections. They are trained to recognise subtle features that may signal instability. Complementing this is our drone operations team, providing geospatial data that compliments both proactive and reactive assessments.
To extend our expertise beyond the cyclical annual inspection programme, we have launched GeoInspections. This service supports the rail industry by combining rope access techniques, vegetation clearance, and our inspection capabilities. With these integrated services, GeoInspections can deliver timely, accurate, and cost-effective geotechnical evaluations.
The trend towards wetter winters and more intense storms is set to continue. Whatever your personal views on global warming and climate change might be, the evidence on the ground is undeniable. The railway’s slopes are under greater strain than ever before. Ensuring their stability requires vigilance, investment, and collaboration.
Earthworks may not capture headlines, but they underpin every journey. As Britain faces an uncertain climate future, one thing is clear: if the railway is to keep the country moving, its foundations must remain secure.
Image credit: GeoAccess