Identification of theoretical parameters used to forecast underground mining impacts to implement long-terms forecasts of underground mining impacts – case study

Abstract

The paper is a case study of ground surface subsidence induced by a long-term mining of hard coal. Knothe prediction model is commonly used in Poland as a technique for prediction of the subsidence-related deformation of ground surface. The presented issue is related to assumptions about the value of the theory parameters in long-term forecasts on the impact of mining on the surface, which are included in the mine development plan. Incorrectly selected values can significantly influence the quality of deformation forecasts. The calculations presented in the article were made for the area where the exploitation of six coal seams lasted more than thirty years. At the same time, deformations of the surface were observed by means of geodetic measurements. Based on the subsidence curves of the observation line points over time, three periods of rock movement decrease were determined. The range of mining operations was determined for the periods of decreased rock movements. The parameters of Knothe’s model were identified on the basis of geodetic measurements for extracted coal seams. Parametric calculations were made for the increasing range of mining operations and for the ranges of operation between subsequent decreases in the movements of the rock mass. Identification of the parameters of the theory thus made it possible to trace changes in the parameter values for different mining ranges. Significant changes were noted for the parameter describing the dispersion of influence (tanβ), while changes in the coefficient of roof control are not significant and their value becomes stable after some time. As the extent of the mining exploitation was increasing, its influence on both parameters (tangent of angle of major influence – tanβ and coefficient of roof control ‘a’) were evaluated. The changes of tanβ values were found to be significant whereas the changes of the ‘a’ coefficient value are negligible and its value seems to be constant after the initial stage of mining.