Shrinking and swelling of the ground (often reported as subsidence) is one of the most damaging geohazards in Britain today, costing the economy an estimated £3 billion over the past decade.
Many soils contain clay minerals that absorb water when wet (making them swell), and lose water as they dry (making them shrink). Many of us see this in our gardens when the ground becomes cracked during the summer, yet becomes 'heavy' in the winter.
This shrink–swell behaviour is controlled by the type and amount of clay in the soil, and by seasonal changes in the soil moisture content (related to rainfall and local drainage).
Ground moisture variations may be related to a number of factors, including weather variations, vegetation effects (particularly growth or removal of trees) and man-made activity. Variation in ground moisture can cause ground movement, particularly in the upper two metres of the ground which may affect building foundations, pipes or services.
A property affected by shrink–swell may experience the following problems:
The potential for shrink–swell to be a hazard has been assessed using 1:50 000 scale digital maps of superficial and bedrock deposits. These have been combined with information from the BGS Superficial Drift Thickness dataset, scientific and engineering reports. The detailed digital data illustrated in the map are available as attributed vector polygons, as raster grids and in spreadsheet format.