Prediction of coal face rockbursts and microseismicity in deep longwall coal mining

Abstract

A new method is proposed for predicting rockbursts, as well as microseismicity in deep longwall coal mining. The method is able to predict failure in the coal seam and in the rock mass by using 3-D elastic numerical stress analyses. These locations were compared with the results of microseismic monitoring. Fracturing intensity and its variation with respect to face advance were represented by the maximum shear seismic moment release rate. The “Seismic Moment Method” was applied to three cases in the Horonai Coal Mine and in the Miike Coal Mine, Japan. The first case considered panels W8-5U and WS-5 in the Horonai Coal Mine at 1055 and 1125m deep. Even though no rockburst occurred, areas where microseismic events were concentrated were predicted. It was also clear, by comparing calculated maximum shear seismic moment release rate to observed data, that the magnitude of the seismicity and its variation with respect to the face advance were also successfully predicted. The second case corresponded to panel W6-3 in the same mine from 915 to 985m deep. Microseismic monitoring had not yet been introduced, however, the rockburst in this panel was successfully predicted as fracturing of coal seam elements at the coal face. The last case considered panels E3–E6 in the Miike Coal Mine at 600 and 650 m deep, respectively. The location and intensity of microseismicity were again predicted; in addition, toppling as well as rockbursts were also predicted. Relations between the extent of the relief zone ahead of the coal face and the occurrence of rockbursts are discussed. An effective method to prevent rockburst hazard is also proposed.