(Figure 3) and complementary stability analysis. In this geomechanical study, the criteria proposed by Nickson et al. (2001) was adopted. Their stability chart incorporates the calculation of the stability number “N,” which makes it particularly suitable for the complex and variable ground conditions encountered at the María Teresa mine. Figure 3 – Sofia D Geomechanical zoning, on the right side the calculated values of “N”. (DCR Ingenieros S.R. Ltda. Geomechanical Study,2018) 2.2 Blast vibration monitoring All blasting operations require precise control to minimize their disruptive effects on nearby structures and the environment. As described earlier, recovery of the secondary stopes at Sofia D employs mass blasting, with radial boreholes drilled in a burden-spacing pattern tailored to the rock mass characteristics. To characterize the propagation of detonation-induced waves and assess their potential impact on exposed CHF walls and overall geomechanical stability, blast vibration monitoring was implemented. Vibration data were collected using seismographs equipped with triaxial geophones, which recorded particle velocity waveforms. Sensors were strategically installed at the undercut level across multiple near-field (typically 10–50 m) and far-field (>50 m) locations relative to the blast source. Measurements of peak particle velocity (PPV) and corresponding scaled distances enabled regression analysis (log-log plot of PPV versus scaled distance) to derive site-specific attenuation constants (K and α) for the ground vibration attenuation law. This followed the widely accepted USBM scaled-distance form: PPV = K . (SD) −α =K . (ඥ D Q)−α (1) Where: PPV: Peak-Particle Velocity (mm/s) SD: Scaled distance D: Distance from the blast source (m) Q: Maximum charge per delay (kg) K: Propagation coefficient
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