Chartered civil engineer Vicky Mastoridou (CEng, MICE), development manager at Groundforce Shorco, explores how contractors are coping with high temperatures below ground, the impact of thermal loading on the foundational phase of projects, and how climate volatility is reshaping UK geotechnical design.
The weather doesn’t lie, the UK construction industry now operates in a far different climate than traditional design baselines were built for.
With Summer 2026 on course to be the UK’s hottest on record, eclipsing the record set just last year, it’s clear temperatures exceeding 30°C, spreading drought and rapidly shifting ground conditions are no longer brief operational disruptions; they represent a permanently altered operational landscape.
The death of historical baselines
Seasons in the UK have historically been very distinct, but as climate change drives more extreme weather, we are seeing more extreme events and greater blending between seasons.
Over recent decades, we have witnessed a run of unusually hot summers, and a shift toward prolonged dry periods punctuated by short, high-intensity rainfall events – with far greater climatic variability between the two.
For contractors trying to get projects “off the ground” with minimal delays, this creates additional challenges that must be addressed.
Clay-rich soils occur across significant parts of England, and where present, they can be highly sensitive to changes in moisture content. During prolonged hot, dry periods, these soils lose moisture and shrink, leading to desiccation cracking, changes in stiffness and strength, and in some cases, ground movement that can affect both foundations and excavations.
When heavy rain follows a dry period, those same soils can then respond very differently. Water exploits these cracks and can penetrate much deeper and faster into the ground, causing localised softening, swelling, and pore water conditions. This repeated cycle of drying and rewetting creates a much more dynamic ground environment that many project managers, contractors or engineers have not had to deal with on such a regular basis.
For temporary works, this means that ground conditions assumed during design may not remain constant throughout the construction phase. Although excavations and their support systems are generally temporary, their performance depends heavily on the behaviour of the surrounding ground.
Rapid or prolonged weather changes can alter the behaviour of the ground around an excavation, sometimes over a relatively short period. This reinforces the importance of site-specific design, regular review of ground conditions and close collaboration between contractors, temporary works designers and specialist suppliers.
Below the surface: What happens when temperatures spike?
When site temperatures rise above 30°C, attention naturally focuses on workforce welfare, hydration, and concrete curing. Yet less visible changes in the ground can pose equally significant risks to temporary works, site safety, and construction programmes.
Extreme heat affects more than the ground; temporary shoring systems holding back excavation walls also undergo severe physical stress.
Exposed structural steelwork (such as heavy-duty hydraulic props, sheet piling, and bracing frames) absorbs direct solar radiation, driving surface temperatures well above ambient air levels. Because these structural members are restrained between retaining walls, walers, and concrete slabs, they cannot freely expand outward. This creates an ‘engineering chain reaction’ across the site.
Thermal expansion increases the internal axial load – the internal squeezing force – effectively trapping the struts inside a giant, invisible vice:
- Steel expands as it heats up. If a prop is restrained by the excavation walls, walers and connections, it cannot expand freely. Depending on the stiffness and behaviour of the overall system, this restraint can increase the compressive force within the prop and transfer additional loading into the retaining structure.
- A strut is installed primarily to retain soil. However, during a 30°C+ heatwave, the strut must fight two forces simultaneously: the ground pushing in, and its own heat expansion pushing out. This consumes the member’s engineered strength reserves much faster than anticipated.
- If these temperature effects are accounted for during the design phase, engineers may specify additional propping or heavier sections to handle peak thermal loads. While this maintains structural safety, it leaves less physical clearance within the excavation pit – impeding plant access, machinery movement, and overall site logistics.
Crucially, these spatial and structural trade-offs can be planned for from the outset, rather than managed reactively under tight site deadlines.
Building resilience
If there is one fundamental transition the UK construction sector must make over the next decade, it is moving from designing around historical weather averages to designing for climate volatility.
The core question for project teams can no longer be “is a heatwave likely during our project?”, but rather, “how will the temporary works perform when one occurs?”
By considering climate-related risks from the outset and incorporating appropriate ground assessment, thermal analysis, inspection and monitoring into temporary works planning. Project teams can make substructure works safer and more resilient during periods of extreme weather.
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