The forecast of mining-induced seismicity and the consequent risk of damage to the excavation in the area of seismic event

The Central Mining Institute has developed a method for forecasting the amount of seismic energy created by tremors induced by mining operations. The results of geophysical measurements of S wave velocity anomalies in a rock mass or the results of analytic calculations of the values of pressure on the horizon of the elastic layers are used in the process of calculating the energy. The calculation program which has been developed and adopted has been modified over recent years and it now enables not only the prediction of the energy of dynamic phenomena induced by mining but also the forecasting of the devastating range of seismic shock. The results obtained from this calculation, usually presented in a more readable graphic form, are useful for the macroscopic evaluation of locations that are potential sources of seismic energy. Forecasting of the maximum energy of seismic shock without prior knowledge of the location of the shock's source, does not allow shock attenuation that results from, for example, a distance of tremor source from the excavation which will be affected by seismic energy, to be taken into consideration. The phenomena of energy dissipation, which is taken into account in the forecasts, create a new quality of assessment of threat to the excavation. The paper presents the principle of a method of forecasting the seismic energy of a shock and the risk of damage to the excavation as a result of the impact of its energy wave. The solution assumes that the source of the energy shock is a resilient layer in which the sum of the gravitational stresses, resulting from natural disturbances and those induced by the conducted or planned mining exploitation, is estimated. The proposed solution assumes a spherical model for the tremor source, for which seismic energy is forecasted as a function of the longwall advance and the elementary value of seismic energy destroying the excavation. Subsequently, the following are calculated for the forecast of the seismic energy of a shock with the defined location of its source: value of the coefficient λ of dispersion/attenuation of seismic energy and the flux of seismic energy at predetermined distances r from the tremor source. The proposed solution for forecasting the seismic energy of tremors and the level of risk of damage to the excavation during the functioning of mining operations is helpful in the development of bump prevention. Changing the intensity of mining operations enables the level of the seismic energy induced by the operations both at the stage of its development and during the excavation of a seam using the longwall method to be “controlled”. The presented solution has been produced for an area disturbed by the mining of coal seam 510 in the hard coal mine, Jas-Mos. An original program developed by CMI was used for the calculations.