Sinkholes forming at the land surface are serious problem posed to the public safety. Their occurrence is related to the collapse of shallow voids that are present inside the rock mass. The caverns may be a result of geological processes, mostly karst phenomena, or occur due to human activity. Depending on the genesis of the caverns, the sinkholes forming above may be classified as natural or of anthropogenic origin (Chudek et al.
1988; Augarde et al.
2003). Numerous publications present cases of sinkhole formation due to the loss of stability of karst voids in many different countries: in Florida, USA (Brinkmann et al.
2008; Xiao et al.
2016), in Maryland, USA (Doctor et al.
2008), in Greece (Barthellos et al.
2012; Papadppoulou et al.
2013), in Russia (Baryakh and Fedoseev
2011) and in China (Jiang et al.
2017). The voids that are formed in the rock mass due to human activity are mine workings—remainings of mining activity conducted in past times at shallow depths. The above may also include voids which formed due to pipeline failures and precipitation (Mellett and MacCarillo
1996; Scarborough
1996). Instances of sinkholes related to old mining workings do not occur only in Poland (Strzałkowski
2019), but also in many other countries including India (Singh and Dhar
1997) and United States (Hunter
2015). The sinkholes forming in mining areas in China constitute an interesting issue, as the changes in hydrological ratios due to exploitation of various minerals (coal, metal ores) lead to the outflow of karst water to the workings. Along with the suffosion phenomenon, this process generates sinkholes at the surface (Li and Zhou
1999). The co-occurrence of both natural and anthropogenic factors may thus be noted.
From the public safety point of view, the assessment of the sinkhole hazard level is significant. Based on that assessment, also the appraisal of suitability of such areas for future economic use may be conducted.
First, it is worth to determine what factors have an impact on the loss of stability of shallow voids. As the causes of the formation of sinkholes in mining areas in India, the authors of the paper (Singh and Dhar
1997) have mentioned: shallow exploitation, tectonic disturbances and the thickness of loose rocks in the overburden. In the paper by (Xiao et al.
2016), a significant impact of atmospheric conditions on the formation of sinkholes has been noted. The impact was manifested mostly by changes in hydrogeological conditions caused by precipitation. Similarly, the dependence between the number of observed sinkholes and the amount of atmospheric precipitation in Upper Silesia has been noted in the paper (Chudek et al.
1988). In Greece, the formation of sinkholes over karst voids was related, i.e., to the seismic activity, although other natural causes were also considered (Papadppoulou et al.
2013). The authors of the paper provide an estimation of sinkhole formation probability based on an analysis of geological conditions in locations where the sinkholes already occurred and—based on that—they predict the occurrence of new sinkholes in areas characterized by similar conditions. In the paper by (Gutiérrez et al.
2008), it has been noted that such extrapolation is not sufficiently verifiable, and thus, proper protection of structures against sinkholes is a better solution. In the paper (Malinowska and Matonóg
2017), the geological conditions that are favourable for the formation of sinkholes and related to human activity have been indicated (the distribution of further exploitations, vibrations due to traffic). In case of separately occurring voids characterized by predictable dimensions and no action of other external factors, calculations may be performed in a relatively simple and reliable method. The problem of predicting the occurrence of sinkholes due to the loss of the load-bearing capacity of old wooden supports, and thus, the loss of the void’s stability, has been considered by Strzałkowski (
2019). The assumption of this solution was the lack of any external factors affecting the void. The prediction of the collapse of a karst cavern with the use of numerical methods has been presented in the paper by (Baryakh and Fedoseev
2011). In complicated conditions of co-occurrence of numerous external factors, the problem is more complex. In the paper (Pilecki
2008), while discussing the application of geophysical methods for studying the locations of shallow voids, it has been established that it is difficult to determine the time and location of the sinkhole formation. It should be kept in mind that sinkholes are one of the forms of underground mining impact on the environment (Kratzsch
1983; Whittaker and Redish
1989; Bell et al.
2000). The purpose of this paper is to exhibit the causes behind seven sinkholes created over mining galleries in cases where several factors co-occurred.