1484 assessment system. At the same time, an increase in the extent of the fractured zone to 7.2 m was observed, indicating progressive loosening of the rock mass structure. Analysis of axial force measurements in the instrumented bolts revealed only a slight increase in bolt loading despite the observed deterioration of roof conditions. This phenomenon was interpreted as a manifestation of localized roof failure that did not result in uniform load transfer to the existing bolting system. The nature and location of the observed deformations indicated that the primary cause of these phenomena was the influence of elevated horizontal stresses acting from the left sidewall of the roadway. In response to these conditions, a decision was made to locally reinforce the support system by installing cable bolts with a load capacity of 420 kN. These bolts were installed at a distance of approximately 0.8 m from the left sidewall, with a spacing of 0.8 m, corresponding to the spacing of rows of previously installed rebar bolts. The adopted solution was intended to increase the load-bearing capacity and stiffness of the support–rock mass system in the zone of maximum stress concentration, as well as to limit further development of roof separations and propagation of the fractured zone. Analogous measures were implemented in the roadway section between chainages 920 m and 1,020 m. In this area, the originally designed basic bolt spacing was 1.0 m; however, due to difficult geomechanical conditions and the need to increase the support safety margin, the bolting system was extended. The support was supplemented with two additional rows of bolts with the same parameters as the primary bolts, as well as two rows of cable bolts equipped with Gifford-type clamps. These cable bolts had a length of 6 m, a diameter of 18 mm, and a minimum load capacity of 320 kN, enabling effective suspension of weakened roof layers to higher-lying, more competent strata of the rock mass. The implemented solutions were consistent with the adopted concept of active response to in situ monitoring results and confirmed the validity of stepwise adaptation of the rock bolt support scheme to actual geological and mining conditions, in accordance with the assumptions of the developed methodology for designing a self-supporting rock bolt system. 5. SUMMARY This paper presents a comprehensive analysis of the stability of a roadway maintained exclusively with a self-supporting rock bolt system, constructed at great depth under conditions of complex geological structure and strong mining-induced influences, based on a case study from the “Budryk” hard coal mine in Poland. The presented investigations represent one of the few case studies of this type involving a roadway driven with a self-supporting rock bolt system at a depth of approximately 900 m, constituting a significant contribution to the advancement of knowledge on the application of such support systems under difficult geological and mining conditions. The study combines detailed laboratory and in-mine analyses of rock strength parameters with an extensive in situ monitoring program, including measurements of fractured zone extent, roof rock separations, roadway convergence, and loads and stress levels in rock bolts. This broad scope of observations enabled a multi-faceted assessment of the interaction between the rock bolt support system and the surrounding rock mass, as well as identification of mechanisms responsible for local deterioration of stability conditions. The results clearly confirmed that the effectiveness of a self-supporting rock bolt system is strongly dependent on local geological and mining conditions. Of particular importance are the quality and stratification of roof rocks, the presence of coal layers in the immediate roof, the degree of rock mass fracturing, and the orientation of the roadway relative to the direction of maximum horizontal stresses. It was demonstrated that unfavourable roadway orientation with respect to the principal horizontal stress component leads to asymmetric development of roof deformations and local stress concentrations, which is directly reflected in the distribution of roof separations and bolt loads. The analyses conducted demonstrated that continuous monitoring of rock mass behaviour and flexible adjustment of the bolting scheme to current conditions are key elements for the safe maintenance of roadways supported by self-supporting rock bolt systems. The application of additional cable bolts in zones characterized by increased fractured zone extent and exceedance of alarm thresholds effectively limited further deformation development and restored the stability of the support–rock mass system.
RkJQdWJsaXNoZXIy MTM0Mzk2