OR/15/021 Appendix 1: Descriptions of the GeoSure hazards

Wildman, G, Adlam, K A M and Cartwright, C E. 2015. User Guide for the GeoSure Insurance Product (version 7). British Geological Survey Internal Report, OR/15/021.

The six Natural Ground Stability hazards assessed by GeoSure are as follows:

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 the activities of people. Such changes can affect building foundations, pipes or services.

Landslides (slope instability)

Slope instability occurs when particular slope characteristics (such as geology, gradient, sources of water, drainage, or the actions of people) combine to make the slope unstable. Downslope movement of materials, such as a landslide or rockfall may cause damage, such as a loss of support to foundations or services or, in rare cases, impact damage to buildings.

Soluble rocks (dissolution)

Ground dissolution occurs when certain types of rocks, containing layers of soluble material, get wet and the soluble material dissolves. This can cause underground cavities to develop. These cavities reduce support to the ground above and can lead to a collapse of overlying rocks.

Compressible ground

Some types of ground may contain layers of very soft materials like peat or some clays. These may compress if loaded by overlying structures, or if the groundwater level changes. This compression may result in depression of the ground surface, potentially disturbing foundations and services.

Collapsible deposits

Some kinds of rocks and soils 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 or services.

Running sand

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