The longwall method is used in many countries around the world in the underground extraction of coal seams. This method enables significantly improved production results to be achieved when compared to the bord and pillar mining system. However, this mining method requires higher capital investment compared to bord and pillar mining. One of the essential elements required to achieve the anticipated level of production from longwall panels is good shield-strata interaction. This means that the shields used in the longwall faces should have an adequate capacity to ensure the maintenance of roof stability in the longwall working. The issue of determining shield capacity has been the goal of research in many countries resulting in a number of different methods for calculating the required capacity of shields. In recent years, numerical modeling and ground reaction curves (GRCs) have been used to determine adequate shield capacity. An important factor to be considered in analyses using the concept of GRC for shield support selection for ground and mining conditions is roof convergence. This paper presents an analysis of shieldroof strata interaction in two longwall panels with natural roof caving in the gob using the concept of GRC. The GRCs for the specific mining conditions in the two longwall faces were determined by means of numerical modeling using Phase 2 software. Performance characteristics of two-leg shields were obtained from underground measurements conducted continuously during the retreat of the longwall panels. In a specially prepared measuring shield, the changes in the leg pressures were measured. In addition, the changes in shield geometry were assessed by means of inclinometers. For the two longwall panels studied, the selected variations of leg pressures and changes of shield height in time are presented for a single shield's cycle during the longwall operations for shield advance, setting, loading, and lowering. An analysis of the interaction between the shield and the roof strata rock mass was performed based on a comparison of the GRC and the operating characteristics of the shield. The values of the roof convergence, which occurred in the longwall faces during the single shield's cycle, are presented. It is strongly recommended that a system enabling the characterization and mining conditions appropriate for shield capacity determination and selection be developed.

The paper presents the results of experimental and model tests of transport of dispersed fluid droplets forming a cloud of aerosol in a stream of air ventilating a selected section of the underground excavation. The excavation selected for testing is part of the ventilation network of the Experimental Mine Barbara of the Central Mining Institute. For given environmental conditions, such as temperature, pressure, relative humidity, and velocity of air, the distribution of aerosol droplet changes in the mixture of air and water vapor along the excavation at a distance was measured at 10 m, 25 m, and 50 m from the source of its emission. The source of aerosol emission in the excavation space was a water nozzle that was located 25 m from the inlet (inlet) of the excavation. The obtained results of in situ tests were related to the results of numerical calculations using computational fluid dynamics (CFD). Numerical calculations were performed using Ansys-Fluent and Ansys-CFX software. The dimensions and geometry of the excavation under investigation are presented. The authors describe the adopted assumptions and conditions for the numerical model and discuss the results of the numerical solution.

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