Mining hazard (not including coal)

Groverake Mine, Weardale.

Great Britain has long and diverse history of mining activity, which has resulted in the extraction of over 60 commodities. Mining activity has ranged from large-scale metal and building-stone mining to small-scale activities supporting local industries, including extraction of jet, ball clay and graphite.

Hazards caused by old mine workings

Historic mining activity has resulted in underground voids that, particularly where shallow, may collapse and cause surface settlement. This can lead to financial loss for anyone involved in the ownership or management of property in former mining areas, including developers, householders and local government.

Costs resulting from the presence of old workings include increased insurance premiums, depressed house prices and, in some cases, engineering works to stabilise land or property. However, armed with knowledge about potential issues, preventative measures can be put in place to alleviate the impact to people and property.

The mining hazard dataset

The BGS mining hazard dataset combines geology, which constrains the distribution of workings, with records obtained through extensive literature searches to identify areas of past working, resulting in a national dataset indicating the likelihood of past underground mining.

Initially the 60 commodities have been grouped into a range of broad categories, including:

  • evaporites
  • chalk
  • vein minerals
  • bedded ores
  • building stones
  • oil shale
  • other commodities including, but not limited to:
    • talc
    • pigments such as raddle or ochre
    • ganister
    • graphite

A second phase of processing collates the data into a single, comprehensive resource showing the location of known (non-coal) mining areas and describes the potential hazard associated with each site.

Zone of influence

Rookhope, Weardale.

Underground workings are surrounded by an area of ground, which is affected by additional stresses due to its proximity to the working, and therefore may be subject to subsidence. The extent of this area is controlled by multiple factors including depth, competence of overlying beds and extent of working. These may however, be partially mitigated by other aspects such as type and depth of working. This area is known as the 'zone of influence' (ZOI).

Zones of influence have been extensively studied in relation to coal mining.The BGS is currently conducting research to explore the calculation of ZOI associated with other types of mining.

Current research will develop a methodology to calculate the potential surface expression of this subsidence area. Initially the study will focus on room-and-pillar mining to obtain an understanding of the mechanisms involved in determining the ZOI.

Case study

The Long Meg gypsum mine in Cumbria has been used to develop a case study with which to establish the methodology. Further testing will be carried out using other evaporite sites and extended to other mining types.

Factors affecting the zone of influence

Several geological and mining parameters affect the nature, magnitude and extent of subsidence and therefore the ZOI. Some of the factors influencing the ZOI, and considered in calculating the dataset include:

Middleton limestone mine, Midlothian
  • seam thickness
  • seam depth
  • dip of seam
  • mine roof or floor competence
  • nature of overburden
  • near-surface geology
  • discontinuities
  • degree of extraction
  • surface topography
  • groundwater levels
  • mined area
  • method of working
  • time elapsed

Other research and development

  • Development of a database of subsidence events including sinkholes and both natural and artificial mine collapse, particularly related to climate-induced occurrences.
  • Continued development of the BGS mine plan collection to support 3D modelling and aid understanding of mining-related subsidence events.

Contact

Contact Kathrine Linley for more information or to get involved.