2141 Table 2. Validity of samples cut from different boreholes Borehole / dataset Lithology Total n Valid Not Valid Validity rate BH1-roof Dolomite 9 5 4 55.6% BH1-roof Anhydrite 17 13 4 76.5% BH3-roof Dolomite 9 8 1 88.9% BH4-roof Dolomite 25 14 11 56.0% BH1-sidewalls Anhydrite 6 4 2 66.7% BH2-sidewalls Anhydrite 6 4 2 66.7% BH3-sidewalls Sandstone 9 8 1 88.9% BH4-sidewalls Sandstone 4 4 0 100% The plot in Figure 4 shows cumulative AE hits versus axial stress σ for dolomite samples extracted from roof strata (BH-3). Most curves, marked green, follow a consistent pattern: a short low-activity phase, then a clear onset of AE (typically ~8–15 MPa), a rapid increase in CumHits up to ~25–30 MPa, and finally a plateau (stabilisation) at different levels (~40–100k hits), reflecting natural material variability and measurement effects (e.g., sensor coupling/threshold). Still, one sample was a clear outlier: it remains almost inactive until ~35 MPa and then shows a strong increase between ~35–50 MPa before reaching a plateau. This right-shifted AE onset is inconsistent with the rest and would artificially bias the estimated Kaiser stress (σK) upward, therefore it was excluded as an outlier. Figure 4 – CumHits vs. axial stress σ for BH3-roof The figure 5 presents the cumulative acoustic emission hits (CumHits) versus axial stress σ during uniaxial loading, illustrating a distinct transition from near-silent behaviour to a rapid increase in AE activity, where the Kaiser point (σK) is identified. 0 20000 40000 60000 80000 100000 120000 0.000 10.000 20.000 30.000 40.000 50.000 60.000 CumHits σ [MPa] Dolomite_0,20 Dolomite_0,45 Dolomite_0,80 Dolomite_0,95 Dolomite_1,65 Dolomite_2.50 Dolomite_3.50 Dolomite_3.75 Dolomite_4.35
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