230 Figure 11 – Map of axial forces in rock bolts on the 385th (final) day of measurements: (a) chainage 564 m, (b) chainage 936 m The results obtained from monitoring of roof rock separations, loads in instrumented rock bolts, and the extent of the fractured zone clearly indicated the need to reinforce the roadway roof with additional rock support elements. In the section between chainages 245 m and 287 m, an intensification of destructive processes in the roof was recorded, manifested by an increase in separation values to approximately 56 mm. This level exceeded the second alarm threshold adopted in the roadway stability 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
RkJQdWJsaXNoZXIy MTM0Mzk2