Shrink–swell hazard potential mapping

GeoSure shrink-swell hazard potential map

 

>3D volume change potential of the London Clay

 

GeoSure is a BGS product which gives an indication of ground stability and the potential for ground movement or subsidence. It includes data for collapsible deposits, compressible ground, landslides (slope instability), running sand, shrink–swell and soluble rocks (dissolution).

The shrink–swell layer is based on properties of both bedrock and superficial deposits and also takes into account areas where bedrock is covered by superficial deposits. The resultant map shows areas susceptible to shrink–swell, with the potential for soil volume change subdivided into very high, high, medium, low or nil.

3D volume change potential mapping, London

All clays are susceptible to some shrinkage and swelling due to changes in moisture content. Those with a higher proportion of expansive clay minerals, such as smectite, are more prone. The amount by which a soil changes in volume as it dries or becomes saturated is known as its Volume Change Potential (VCP) and this in turn is reflected by shrinkage and swelling of the ground. The VCP indicates the potential of a soil to change in volume due to a change in soil moisture. Soils with high or very high VCP may easily cause damage to foundations with a small volume change. Soils with low or medium VCP are not likely to expand or shrink by a damaging amount, under normal situations, but may experience such a change in extreme conditions.

Using BGS data, from the National Geotechnical Database, a 3D model for the VCP of the London Clay Formation has been created. This has revealed a significant geographical trend in the volume change potential of the deposit, confirming an overall increase in plasticity from west to east, but also showing subtle trends with depth. When the VCP values for the London and Hampshire Basins are examined, the results show major differences in the values for the London Clay basin and the Hampshire Basin.

Selected References

Harrison, M, Jones, L D, Gibson, A, Cooper, A, Wildman, G and Foster C. 2009. GeoSure Version 5. Methodology Review: Shrink Swell British Geological Survey Internal Report IR/08/092: 31pp.

Jones, L D and Terrington, R. 2009. Modelling Volume Change Potential in the London Clay. Quarterly Journal of Engineering Geology and Hydrology IN PRESS

Jones, L D and Hobbs, P R N. 2004. The Shrinkage and Swelling Behaviour of UK Soils: Clays of the Lambeth Group. British Geological Survey Research Report RR/04/01

Jones, L D and Hobbs, P R N. 1998. The Shrinkage and Swelling Behaviour of UK Soils: Mercia Mudstone. British Geological Survey Technical Report Series No. WN/98/14

Jones, L D and Hobbs, P R N. 1998. The Shrinkage and Swelling Behaviour of UK Soils: Gault Clay. British Geological Survey Technical Report Series No. WN/98/14

Contact

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