Subsidence problems due to abandoned pillar workings in coal seams

Abandoned mine works are a potential cause of ground subsidence and hence are of major concern where development or re-development is to take place. In the United Kingdom, information necessary to locate potential hazards may be available but occurs in numerous scattered locations and it may require considerable time to access the data. In recent years thematic geological maps have been produced for some of the British coal field areas. The paper describes the historical evolution of the mining system, emphasising the pillar workings which began in the sixteenth century. Methods of investigation such as downhole hammer and geophysics are briefly mentioned and the importance of zoning the land discussed. Stabilisation measures may involve occupying the workings with hydraulically-emplaced fill or cheap bulk grout. In areas of less risk, special foundation structures may be used.