Effects of abandoned shallow bord-and-pillar coal workings on surface development

The relevance and potential effects of the factor of safety, time and subsi dence are considered in the context of abandoned bord-and-pillar mines. Sta bility during the period of underground mining safety is normally assured b y use of a safety factor, but calculation of the time to failure of the pil lars when a mine is abandoned has not been adequately addressed in the lite rature. Coal pillar information gathered from a worldwide review was subjec ted to statistical analysis and a method for the assessment of stability, l inking factor of safety to time, subsidence to rock mass rating and the ext ent of surface subsidence to peak pillar vertical stress was developed for spreadsheet application. Factors of safety for a proposed development shoul d be site-specific to the form of development; general factors of safety sh ould not be used. Where a desired factor of safety cannot be met measures t o secure the site will be required.