Simple method for the identification of subsidence susceptibility above underground coal mines in Korea

Estimation of subsidence susceptibility due to mining is a primary task for the effective and economical management of subsidence. If the status of an underground mine is well known, this process is simple and clear. Unfortunately, in Korea, the excavation shape is typically complicated because of the complex geological characteristics and corresponding mining methods, and relevant data on abandoned or closed coal mines are often deficient. Therefore, estimation methods developed elsewhere are usually not suited to Korean coal mines. To solve this problem, we developed a quick, simple and quantitative method suitable for the estimation of subsidence susceptibility prior to the detailed field investigation of coal mines. Gangway depth from the surface and the attitude (dip and dip direction) of main geological features were selected as input data based on the degree of availability and reliability, and the gangway was represented as a series of points instead of closed polygons for easy calculation. Two core assumptions of this method were that the susceptibility to subsidence within a unit area increases as i) the depth of the gangway from the surface decreases and ii) the number of gangways below the unit area increases. In spite of the simplicity of this method, it gave satisfactory results when applied to one virtual excavation model and two closed coal mines where subsidences had occurred.