1460 rock-mass) parameters adopted for the excavation horizon are summarized in Table 2. Table 2 - Calibrated rock and rock-mass parameters adopted for the excavation horizon (final input values used in the numerical model). Nonlinear parameters for calculations Undisturbed rock mass Large pillars Technological pillars Goaf’s zone (pillars 3×4) 1st iteration of calculations ()* 100 90 80 70 '$ 8 5.4931 3.6175 2.0963 + 1.0 0.3168 0.0925 0.0214 , 0.0 0.1 0.2 0.4 - 0.5 0.5002 0.5006 0.5014 " 33.50 30.27 25.52 16.48 # 9.7328 5.93 3.95 2.75 . 39.84 38.42 35.94 32 2nd iteration of calculations ()* 100 95 90 60 '$ 8 6.6291 5.4376 1.3414 + 1.0 0.5629 0.3105 0.0059 , 0.0 0.1 0.15 0.4 - 0.5 0.5001 0.5002 0.5028 " 33.50 31.05 29.36 10.50 # 9.7328 7.54 5.8959 2.1657 . 39.84 39.24 38.35 28.60 3rd iteration of calculations ()* 100 95 90 60 '$ 8 6.6291 5.4376 1.1909 + 1.0 0.5629 0.3105 0.0048 , 0.0 0.1 0.15 0.5 - 0.5 0.5001 0.5002 0.5028 " 33.50 31.05 24.15 9.10 # 9.7328 7.54 5.8959 2.0641 . 39.84 39.24 38.35 27.67 3. FEM BASED SELECTION OF THE OPTIMAL EXPLOITATION METHOD Using the calibrated 3D FEM model, the spatial distribution of stresses and safety factors was analysed for three pillar-size variants (4×4 m, 5×6 m, 8×8 m) across successive mining stages. For interpretation, the safety factor (SF) was adopted as the primary indicator: values SF < 1 denote a risk of instability, whereas SF ≥ 1 indicates stable conditions. The results are presented along the reference crosssection A–A′ (Figure 8), covering the transition from undisturbed rock mass through the active mining front to the mined-out/liquidation zone.
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