The issues covered by the work are important and topical as sinkholes that develop in large numbers over shallow mining excavations pose a great threat to public safety. In Upper Silesia (Poland), the formation of sinkholes can be observed even for a period of over 100 years following the termination of mining works. An effective method of risk elimination consists of filling the voids with a binding material with strength properties similar to those of the rocks surrounding the void. The application of fly ash is very suitable for this purpose, the use of which also has an ecological aspect. The literature studies presented in the paper indicate the possibility of making mixtures with the use of fly ash that has the required strength parameters. The compressive strength of the mixtures after solidification is up to 3 MPa, or even up to 7 MPa, and in some cases, up to 15 MPa. Most of the voids at shallow depths are found in coal seams, in which the compressive strength at shallow depths amounts to approx. 5 MPa. Thus, by filling the void with such material, we can ensure conditions similar to those prevailing before the excavation was made. The paper presents a case study involving the formation of a sinkhole above a dog heading and an ex post forecast made with the use of two selected methods. These methods yielded results affirming that the development of a sinkhole in the considered conditions is certain. Then, using the said methods, the impact of the filling level of the void on the possibility of sinkhole development was analyzed. The obtained results indicated the necessity to fill the void to around 90% with the use of one of the methods and its complete filling with the use of the other method.

The article presents subject matter related to the assessment of the suitability of the built-up area, including the occurrence of sinkholes on the surface. The investment plot, which is the subject of the analysis, is located in the central part of the Upper Silesian Coal Basin, where shallow exploitation of coal seams was conducted in the past. At present it is a post-mining area, located at a large distance from active mines. It has an attractive administrative location and good transport connection with the main road connecting the cities of the Silesian agglomeration. These advantages make it particularly attractive in terms of use for various types of investments. The geological and mining factors are not favorable in the area in question, mainly due to the shallow mining exploitation conducted in the past and the access excavations on small depth and an unknown method of liquidation. These reasons are the cause of some restrictions in the use of construction, for which taking the appropriate solutions is recommended. According to the study of (Rules... 2009), the category of mining land should be defined for the areas of liquidated mining plants due to the limitation in construction use. The authors of the article made an attempt to determine it, and they analyzed the geological and mining conditions for this purpose, mainly including mining exploitation conducted in the past. On the basis of the obtained results and own experience, the type of expected hazards and its assessment were determined The probability of the occurrence of the inclusions according to the Chudek-Olaszowski method (Chudek et al. 1988) was assumed as a measure of the hazard.

In the Upper Silesian Coal Basin (Poland), numerous former workings have been left unprotected after the liquidation of mines in the 19th and the beginning of the 20th century. The workings have been located at low depths. The paper presents the results of strength tests of wood samples acquired from linings in former workings, and the obtained results have been compared to the results achieved in tests of samples of wood intended to be used in a reconstruction of a historic gallery. The tests consisted in determining the bending strength of wood in compliance with the applicable Polish standard. The results showed that the wood from historic mines was characterised by high variability of bending strength – usually much lower than that of the wood intended for construction. Too low bending strength of timber may result in caving in shallow excavation and lead to sinkhole creation on the surface.