Performance of dynamic reinforcements to restrain remote triggered strainburst associated failure: Fid-Bau Portal

Performance of dynamic reinforcements to restrain remote triggered strainburst associated failure

Kabwe, Eugie

Graphical abstract Display Omitted

Highlights • Underground crosscut faced abrupt rock fragment ejection ascribed to strainburst. • Appropriate support elements are SECTA cable, D47MDX and ∅22 D-bolt yieldable bolts. • Integrated dynamic support system selected to restrain future strainburst damage. • Bolt’s axial force and elongation results less designed capacity and rupture strain. • Yieldable rockbolt’s performance results considered compatibility acceptable.

Abstract Strainburst occurrence in underground mines is associated with highly stressed brittle and stiff rockmasses which instantaneously dissipate excess strain energy. This strainburst mechanism is difficult to predict in terms of its occurrence, location, and intensity, and so ground control practitioners/researchers devise the appropriate dynamic support system for its associated failure restraint. This paper outlines the back-analysis and dynamic support scheme design for an underground crosscut exposed to a dynamically loaded strainburst that initiated rock fragment ejections. The outline involves a preliminary Institute of Mine Seismology (IMS) seismic intensity measure, strain energy empirical evaluation, and an explicit numerical simulation to determine the static stress concentration and dynamic support scheme performance. The numerical simulation conducted in FLAC^3D employs the advanced strain-softening IMASS constitutive model governed by two Hoek-Brown (HB) bounding yield surfaces (peak and residual). To account for the post-peak brittleness response associated with the strainburst mechanism, the plastic shear strain multiplier ( $ε_{c r i t}$ ) is adjusted to 0.0 < $ε_{c r i t}$ < 1.0 with its value closer to 0.0 for high material brittleness. The back-analysis draws that the occurrence was initiated by a low-intensity seismic wave which superimposed an extra stress component to the initial static stress consequently, triggering the rock fragment ejections. Therefore, the appropriate dynamic support scheme of Weldmesh Fibrecrete, SECTA cable, D47 MDX and $\emptyset$ 22 D-bolt yieldable bolts is presented to restrain its associated damage. Furthermore, the yieldable bolt’s efficacy is numerically evaluated based on the axial force and elongation capacities which are compared with the published manufacturer’s specifications data. Finally, the results attained from the efficacy evaluation show that the maximum bolt axial force (2 %) and elongation (6 %) are below the manufacturer’s designed capacity and rupture strain therefore their compatibility is deemed acceptable.