Clay soils are susceptible to shrinking and swelling, and the associated change in volume is one of the causes of subsidence, which is visible when cracks appear in our buildings.
Clay soils (e.g. the London Clay, a geological formation very susceptible to volume change) are found in many areas of the UK, but are most common in the London area and in the south east of England.
If we have a wet day, does that mean the ground becomes saturated and any concerns of subsidence due to shrinking and swelling clays are out the window?
Unfortunately not, similarly, when we have a warm sunny day, it does not mean the soil will dry out and cracks will start to appear in the ground and our homes!
Research recently carried out, investigating the controlling factors of shrink-swell properties of clays, has found that the preceding two years of rainfall has a strong influence on the ground saturation, and thus the potential of subsidence in our buildings.
So a rainy day, even a rainy month, has to be considered within the context of the rainfall of the preceding two-year period, to assess the potential of shrink swell today. Once the two-yearly period of rainfall is calculated, only then does this start to give us an indication of the moisture within the ground and the susceptibility of shrinkage. The research has enabled thresholds in rainfall values to be established that suggest high, medium or low likelihood of shrinkage and subsidence occurrence.
Temperature has also been found to be influential, with higher temperatures causing more evaporation and evapotranspiration, leading to further drying and shrinking soils.
Looking to the future, warmer, drier summers and increases in annual temperature and rainfall variability are suggested for the UK. What is considered a heat wave today, is likely to be the norm in the 2050s and cool in the 2080s!
By combining the BGS GeoSure dataset, and applying the UK Climate Projections (UKCP) scenarios for rainfall and temperature changes in the UK for the next century, maps have been produced for the south-east of England showing areas with varying vulnerability to shrink swell and thus subsidence in the future due to climate change. The maps show that areas with clay soils that shrink and swell with changes in moisture are going to become increasing susceptible in the coming century and beyond.
This research outlined above has been published in the following journal article:
Harrison, A M, Plim, J F M, Harrison, M, Jones, L D, and Culshaw, M G. 2012. The relationship between shrink–swell occurrence and climate in south-east England. Proceedings of the Geologists' Association, Vol. 123, 556–575.
Anna Harrison was awarded the Lloyd’s Science of Risk runner-up Prize in the category of Climate Change, for research into the relationship between climate change and clay shrink-swell. The judging panel recognised the originality of its research and felt it highlighted a major emerging risk.
Contact Anna Harrison for more information.