202 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 cross-section 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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