Strata Movement at the Mining Horizon

Abstract

The field of subsidence engineering stretches from the firm rock at the mining horizon to the surface layer of loose ground on which buildings stand and farming is conducted. The cavity artificially created underground by the extraction of mineral removes the natural support from the overlying strata. As a result, successive layers of rock over the mine workings bend under the influence of gravity, until finally the movement reaches the upper earth surface. At the same time, the underground cavity is closed up to a greater or lesser degree. The extent of movement in the upper layers thus depends on the closing up, over a period of time, of this cavity. The size of the latter is consequently the basic dimension in the calculation of strata and ground movement. By contrast, convergence between roof and floor in mine roadways plays only a minor part in movements occurring in the upper layers of overlying rock, because of the insignificant width of roadways.