Subsidence

Subsidence can be caused by certain types of soils, for example clay shrinks and swells according to moisture content. It can also be exacerbated by the effect of trees extending their roots in search of water during prolonged dry periods and by leaking drains washing away the ground under the foundations of buildings. Most of Great Britain has the potential to be affected by swelling and shrinking clay, although the problem is more widespread in the south and east of England where clay rich layers are near the surface. That of course, also coincides with some of the most populous areas.

Global climate change will continue to cause significant change to our weather patterns in the UK. It is predicted that the average UK summer temperature could be up to 2.4°C warmer by 2050. This may cause increased clay shrinkage and additional root spread from vegetation seeking moisture. Equally, an increase in flooding events which put additional pressure on drains could lead to more erosion of sub-foundation material. Unless significant action is taken in the planning of new property development to ensure that foundations are designed to cope with periods of drought and that only certain types of tree are planted close to buildings, the cost of subsidence claims could double by that time, according to the Association of British Insurers – A Changing Climate for Insurance, June 2004.

Understanding geology is vital when determining the stability (and thus value) of land, property, and the safety of its occupiers. The GeoSure data sets from the British Geological Survey provide information about potential ground movement or subsidence in a helpful and user-friendly format. GeoSure national data sets give you valuable information about:

Soluble rocks (dissolution)

Ground dissolution occurs when certain types of rock contain layers of material that may dissolve if they get wet. This can cause underground cavities to develop. These cavities reduce support to the ground above and can lead to a collapse of overlying rocks.

Shrink swell

Swelling Clays can change volume due to variation in moisture, this can cause ground movement, particularly in the upper two metres of the ground that may affect many foundations. 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. Such changes can affect building foundations, pipes or services.

Landslides (slope instability)

Landslide hazard occurs due to particular slope characteristics (such as geology, gradient, sources of water, drainage, man-made constructions) combining to cause the slope to become unstable. Downslope movement of materials, such as a landslide or rockfall may lead to a loss of support and damage to buildings.

Compressible ground

Some types of ground, may contain layers of very soft materials like clay or peat. These may compress if loaded by overlying structures, or if the groundwater level changes, potentially resulting in depression of the ground and disturbance of foundations.

Running sand

Some rocks can contain loosely packed sandy layers that can become fluidised by water flowing through them. Such sands can ‘run’, removing support from overlying buildings and causing potential damage.

Collapsible deposits

Some kinds of rocks may collapse when a load (such as a building or road traffic) is placed on them, especially when they become saturated. Such collapse may cause damage to overlying property.