1476 increase operating costs. Consequently, these conditions differ substantially from those encountered in underground hard coal mining in many other countries, where mining depths typically range from 400 to 600 m and rock bolting systems are predominant (Craig et al., 2021; Li, 2017). Rock bolt support systems are characterized by lower steel consumption, easier underground transportation, and lower costs compared to traditional steel supports. When appropriately mechanized, they also enable higher advance rates (Masny & Ficek, 2021). Additional advantages include improved safety and working conditions, as well as the possibility of full mechanization of the installation process (Ma et al., 2020; Korski & Majcher, 2021). To verify the design assumptions and the effectiveness of the support system, in situ monitoring is typically conducted (Małkowski et al., 2020). For these reasons, roadway development using a self-supporting rock bolt system installed with a Bolter Miner was implemented at the “Budryk” hard coal mine in Poland. This represented a global first, as the roadway was driven at a depth of approximately 900 m. The aim of this study is to demonstrate how the roadway was successfully maintained using ongoing in-mine investigations of rock mass properties and continuous monitoring of roof strata behavior and installed rock bolts. 2. DESIGN OF A SELF-SUPPORTING ROCK BOLT SYSTEM Proper support design is crucial to ensuring the stability and functionality of underground mine workings throughout their entire service life. Regardless of the design approach applied—analytical, empirical, or numerical—it is essential to consider a comprehensive set of data encompassing natural, technological, and mining-related factors. Of particular importance is the identification of the in situ stress state of the rock mass, resulting from overburden weight, rock properties, and tectonic processes. This stress state determines the secondary stress redistribution after excavation and, consequently, the extent of the rock damage zone surrounding the opening as well as the intensity of deformations. Studies have shown that at greater depths, horizontal stresses may reach values comparable to or even exceeding vertical stresses, which has a significant impact on roadway stability and support loading (Gray & Gibbon, 2023). Understanding the magnitudes and orientations of these stresses has led to the development of the concept of directional mining, which involves driving roadways parallel to the maximum horizontal stress component. This approach reduces the extent of damaged zones and increases excavation advance rates (Mark, 2001). Technological and mining factors are also of considerable importance, including the selection of bolt type, length, spacing, and installation method. Experience indicates that the effectiveness of rock bolt support depends not only on bolt length but also on bolt differentiation, orientation, and the justification for applying pretension, which depends on the bolt type and the degree of rock mass fracturing. In addition, under Polish mining conditions, the stability of underground roadways is significantly affected by the edges of previously extracted seams located above, the number of which may reach up to twenty. These generate a pronounced increase in stresses within the rock mass of underlying seams. Currently, the design of rock bolt support systems increasingly combines empirical approaches (such as the use of geotechnical classifications, e.g., RMR or GSI), analytical methods, and numerical modelling, with particular emphasis on the analysis of monitoring results and their statistical interpretation (Nicholson, 2016). All these approaches, however, require detailed identification of the geomechanical properties of the rock mass, including rock strength, deformability, bedding, discontinuities, and resistance to water action (Małkowski et al., 2016; Bednarek & Mejcherczyk, 2020). These parameters, determined through laboratory and in situ investigations, exhibit significant variability and therefore require regular verification. It should be noted that simplified loading models and empirical methods for determining the extent of the fractured zone were developed for shallower mining conditions, typically at depths of 400– 600 m (Barczyk et al., 2001). At present, these approaches are no longer applied due to their limited consideration of influencing factors, particularly the lack of reference to actual stress conditions and the averaging of geomechanical parameters of rocks surrounding mine workings. Given the great mining depth, variability of rock properties, and the presence of numerous mining and geological factors—such as the edges of overlying extracted seams or faults—only continuous analysis of roadway behaviour can ensure its proper maintenance.
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