## 4 Discussion
The critical panel is defined as the width of an extracted panel for which the maximum possible subsidence should occur at one point. The critical width depends upon the geological characteristics of the overburden. In single seam coal mining operations in New South Wales, Australia, the critical value is typically 1-1.6 times the depth of the overburden [38; 77]. In Europe (including Germany, Poland, and the Czech Republic) [78] it is estimated that a full subsidence trough will form for an extracted space that meets the condition d \(\geq\) 2R, where R is the radius of main influence range determined by the formula \(R=H\cdot c\ell\beta\), and d is the shorter dimension of the coal longwall (width or length). This means that the condition for the occurrence of a full subsidence trough is related to the mining depth (H) and the angle of the main influence range (\(\beta\)), whose values should consider the quality and structure of the rock mass. However, describing the rock mass with a single parameter is a challenging task. Therefore, numerical analyses that consider the structure and tectonics of the rock mass allow for a more accurate description of its behavior. As shown by further geodetic measurements, the increase in the exploited area by panel LW502 led to a significant increase in the subsidence indicator (compared to the results obtained for panel LW501). Research carried out so far indicates that in order to properly model the subsidence basin caused by mining, an anisotropic model should be used. Elastic-plastic models are used in the literature. It should be borne in mind that these models allow for high consistency of the modelled subsidence compared to those observed from measurements. However, these models have a big problem with reflecting the range of the main influences \(R\). In most cases, this range is obtained as significantly exceeding the values observed in reality (overestimated). The situation is similar in the case of horizontal displacements, which also deviate significantly from the measured values. The use of an anisotropic model allows to limit the value of \(R\) obtained from numerical models. However, it is very difficult to determine all the parameter values describing this model. Therefore, the authors use a simplified transversally isotropic model, which has only 5 parameter values (see Section 2.3). The problems with this model are:  
1. Proper selection of parameter values, for this reason the authors used a solution used in science, which allows determining the elastic parameters G\({}_{12}\) and G\({}_{13}\) = G\({}_{23}\), which are difficult to determine for mining conditions. 2. Unfortunately, this model still incorrectly determines the values of horizontal displacements (like other models presented in the literature). Research [79] suggested that the use of contact between the modelled layers allows solving this problem, but these studies did not provide a clear solution (for which layers contact should be used, what friction coefficients should be used, etc.). For this reason, the authors did not take into account the change in friction values and the use of contact between layers in the described tests. Research on this issue will be the subject of further research by the authors. Further numerical analyses based on FEM and the custom script continued to demonstrate high matching accuracy and allowed the determination of the parameters of the rock layers.