The role of geophysical methods in the estimation of sinkhole threat in the post-mining areas of shallow exploitation in the Upper Silesian Coal Basin, Poland

The main aim of the paper is to present a methodology for recognition of destructive processes induced by voids and loosening zone in rock mass by geophysical methods. That recognition has a particular meaning in the estimation of sinkhole threat in the areas of post-mining exploitation of different deposits. Presence of a non back-filled void or discontinuity induced by mining creates unspecified in time risk for the surface area. Discontinuous deformations occur not always over the area where shallow deposit exploitation took place. Time and place of their occurrence are difficult to predict. Deformations observed till now in areas of shallow exploitation in GZW (Upper Silesian Coal Basin) and Olkusz region occurred shortly after mining activities closing and, as late as, over hundred years after. Geophysical researches, because of their measurement and interpretation capabilities, require distinct changes in physical properties of a rock mass. Those changes should be greater than errors and uncertainties of measurements carried out in particular conditions. The theoretical basis of geophysical recognition has been presented in the paper, as well as examples of that method use in the area of Upper Silesian Coal Basin in Poland. Specific features of geophysical investigations with reference to their measurement and interpretation possibilities are discussed. The methodology for recognition of the degree and range of terrain surface threat with discontinuous deformations in post-mining areas has been presented. This method consists in carrying out appropriately designed geophysical investigations and their control by means of drillings and special measurements in the borehole. The paper presents detailed methodology for selected geophysical measurements performed in geological-mining conditions of the GZW. The effect of geophysical work consists of as wide as possible information aquisition, which is to be used for optimal designing of subsurface protection in the areas of shallow mining threatened with discontinuous deformations.