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.

Humic substances are ubiquitous in terrestrial and aquatic ecosystems. Humic acids (HAs) actively interact with organic and inorganic components of lake sediments. This interaction depends on the molecular structure and elemental composition of HAs. The presented research focuses on the investigation of the composition and molecular structure of humic acids isolated from lakes located in the Lena Delta in the Russian Arctic. The findings of the research are needed to estimate the potential capacity of humic acids to bind microelements, particularly toxic metals, in stable compounds. Surface sediment samples (0–10 cm) were collected from 8 lakes by Van Veen grab during the summer period of the “Expedition LENA 2019”. We analyzed elemental composition of the HAs samples. The results showed that the studied HAs of lake sediments are characterized by low nitrogen content and prevalence of aliphatic fragments in their molecular structure. Furthermore, it was found that the studied humic acids are less mature, showing mineralization processes dominant over humification, and have relatively low potential to complexation compared with soils of the Lena Delta as well as lake sediments of territories with more boreal climate conditions.

The paper presents the influence of different liquid cargo properties on discharge rate of hydraulic submerged cargo pumps on modern product and chemical tankers is presented in the paper. Main parts of submerged cargo pumps and hydraulic drive system are described. Some examples of technical solutions of the described systems installed on board of the newly building constructed ship m/t ‘Helix’ are presented. The formula of use application of flow and drive characteristics of cargo pumps is given. These characteristics were made derived for a basic cargo (fresh water) for the case of the service of a real cargo of different viscosity and density.