BGS GeoSure Hazard Categories
Collapsible rocks
These rocks usually consist of with a low density and an open structure that means they can become unstable, when a critical load is exceeded or the material is saturated under load, resulting in a sudden collapse. Their fine-grained nature may make the rocks susceptible to heave as a result of frost action in some conditions.
Compressible ground
Weak ground compresses when a load, such as a house is placed on it. Typically the house will sink into the ground. If the ground compresses unevenly the house will crack and suffer greater damage.
Landslides (slope instability)
A landslide is the outward and downward movement of rock or soil on a slope. Many landslides are mapped and their presence known, however there are many other locations that are also at risk for which no slope movement has been recorded. A small change in drainage or an increased loading due to the weight of a new structure could trigger a landslide in a previously stable area.
Running sand
Running sand is the flow of sand into an excavation or void due to water pressure. Problems commonly occur when excavations meet the water table causing water to flush sand into the excavation. Potentially more hazardous is the break through of deep excavations or tunnels into water-saturated sands causing the water and sand to flow rapidly into the excavation.
Shrink swell
Clay that absorbs water may be a significant hazard to buildings and structures due to its ability to shrink or swell with seasonal changes in water content. Local changes such as leaks from water pipes or drains, or following the removal, planting or severe pruning of trees can also cause these clays to swell or shrink.
Soluble rocks (dissolution)
Parts of Britain are underlain by soluble rocks that can dissolve causing subsidence. These rocks vary from moderately soluble limestone and chalk to highly soluble gypsum and salt. All these rocks can dissolve and create surface depressions, an uneven buried rock surface or underground caves and cavities.
Overview maps of the GeoSure hazards across Great Britain:
The attached FREE British Geological Survey GeoSure overview maps are a superb source of information in themselves. They provide an excellent summary of the GeoSure Ground Stability categories and their ratings across the British Isles.
