transition from low activity to a rapid increase in cumulative hits, and when the detected Kaiser stress met basic quality criteria (identified σK, sufficient total hits, and σK not occurring too close to peak stress). During pilot tests a substantial share of specimens was classified as non-valid (around one third of the dataset). This is important, because it shows that the method is sensitive to sample quality and stress-memory preservation. Several practical factors can explain non-valid behaviour. Stress memory may be weakened by excavation disturbance and unloading close to openings, especially for shallow boreholes. It may also be affected by mining technology and operational impacts, including blasting with explosives and vibration-related microcracking. In addition, long storage time and handling can promote drying, microcrack growth, and progressive degradation of the “memory” signal. Sensor coupling and test setup can further influence the clarity of the Kaiser onset. Despite these limitations, the results show a consistent trend: data reliability improves with depth. The deeper core intervals tend to give clearer Kaiser points and more coherent σK values, while shallow intervals more often produce ambiguous onsets or unrealistically low estimates. This pattern is consistent with a transition from a stressrelieved zone near excavations toward more representative far-field conditions. Based on this observation, future campaigns should prioritize boreholes of at least ~10 m to reduce negative influence and to lower the share of non-valid specimens. The lithology contrast is also visible. Compact carbonates generally produced clearer Kaiser behaviour, while sandstones were more problematic in interpretation, even when the tests were formally “valid.” In particular, very low σK from shallow sidewall sandstone likely reflects local stress relief rather than regional horizontal stress. This highlights a key point for practice: validity criteria ensure a detectable AE change, but they do not guarantee that the estimated stress is representative of the in-situ field. In the next step, we will extend the analysis by calculating the Felicity ratio. This is recommended because it provides an independent measure of stress-memory quality during cyclic loading. It helps quantify whether AE re-activation occurs below the previous maximum stress (damage accumulation or disturbed memory) or close to it (strong Kaiser behaviour). In practice, Felicity ratio can strengthen quality control, support objective screening of disturbed specimens, and improve confidence in stress estimates when the Kaiser point is weak or not unique. 4. CONCLUSIONS In this pilot study, oriented core specimens were tested to check if AE stressmemory methods can support in-situ stress estimation in Polish deep underground mining conditions. Cylindrical samples were prepared from cores taken from four roof boreholes and four sidewall boreholes. The tested lithologies were dolomite and anhydrite (roof) and anhydrite and sandstone (sidewalls). Specimens were loaded along the core axis in cyclic UCS tests using a Walter + Bai DP 100 S testing machine with a ZEPWN CL18 load cell, while AE was recorded with an AMSY-6 (Vallen) system equipped with VS900-M/VS45H sensors and processed in Vallen AE Suite.
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