Post-mining deformations that occur on the surface pose a significant threat to natural environments and urbanized areas. Preventing the effects of deformation is a significant challenge for specialists in geotechnical and civil engineering. Geomaterials, such as geosynthetics or geopolymers, could minimize the damage that occurs. The first section of the article explores the securing of an area, strengthening the rock mass with geosynthetic materials. We provide descriptions of the properties of these materials and the method surrounding their introduction into the soil. The second section presents the research problem, i.e., we describe the damage caused by underground mining. In the last section, we propose a solution for securing the ground with the use of geogrids and geopolymer injections into the rock mass. The analyses led us to conclude that an area subjected to mining influences may be strengthened by the use of geosynthetic materials. The use of geosynthetics in a mining area is a well-known topic, but the additional use of geopolymers may be innovative. Research is still being conducted on the use of geopolymers to fill post-mining voids, in combination with geosynthetics.
This paper presents the results of investigating shallow rock mass layers with the use of electrical resistivity tomography. The aim of the study was to assess the condition of near-surface rock mass layers located above shallow mining workings of a historical mine in view of the possibility of the occurrence of loose zones or possible voids that could pose a sinkhole hazard for the surface. The study was carried out under the conditions of the “Sztygarka” Training Mine and Museum in Dąbrowa Górnicza City (Upper Silesian Coal Basin, Poland), where discontinuous surface deformations occurred in the past in the form of sinkholes. The study and its interpretation indicate the existence of a sinkhole hazard due to the ongoing processes of the transformation of the near-surface rock mass layers above the shallow workings of a historical mine.
The article presents an example of using the electrical resistivity tomography method to assess the condition of shallow rock mass layers in the area of linear discontinuous deformations created in the past due to underground mining activity. The research concerned the mining area of one of the Upper Silesian Coal Basin mines, where intensive mining operations have been conducted for several decades. In the considered area, linear discontinuous deformations were created in the form of ground steps. Their location is related to characteristic layout of deposit accessing roadways and extraction fronts in several coal seams. The article analyzes the geological structure of the deposit and the state of deformation of the rock mass caused by mining operations. In order to evaluate the hitherto impacts, appropriate calculations of the extraction influence were performed, assuming different views on the summation of horizontal strain in long time intervals. The calculations were carried out using the theory of W.Budryk - S. Knothe. Theoretical considerations were supplemented with geophysical surveys performed with using electrical resistivity tomography. Obtained results of the near-surface layers ERT imaging in the form of resistivity profiles confirm the existence of rock loosening zones in the areas of discontinuous deformations occurrence.
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.
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