The purpose of this study was to confirm the existence of acoustic emission (AE) Kaiser effect (KE) in Estonian oil shale (OS), and compare the respective data obtained about working mine pillars. The KE of acoustic emission, a phenomenon with a potential for in-situ stress estimation, can be used for quantifying the damage levels of pillars, and possibly even to measure the state of stress within a pillar. The main role of measurements is to confirm estimated stresses, as the estimation is quite simple in regions of sedimentary rocks. The performed tests showed that the Kaiser effect did exist in oil shale material, at the same time, the low material strength also lowered the feasible stress limit for KE-based stress measurements. Tests were made with inspection of the formula for changes of long-term rock durability in the Estonian oil shale formation. On the basis of the obtained results, the AE method can be used to estimate the long-term rock durability for pillars in conditions of Estonian oil shale mines.
1. Valgma, I., Reinsalu, E., Sabanov, S., Karu, V. Quality control of oil shale production in Estonian mines. Oil Shale, 2010, 27(3), 239–249.
https://doi.org/10.3176/oil.2010.3.05
2. Reinsalu, E., Anepaio, A., Karu, V., Lüütre, E., Roots, R., Saarnak, M., Sein, O., Väizene, V. The Mechanical Properties of Weak Stratified Rocks, 2014 (in Estonian). https://www.researchgate.net/publication/262677053_NORKADE_ KIHILISTE_KIVIMITE_TUGEVUSOMADUSED
3. Undusk, V. Safety factor of pillars. Oil Shale, 1998, 15(2S), 157–164.
4. Stetsenko, V. Investigations on the Support of Non-Homogeneous Roof. Thesis Cand. Sci. (Ph.D.). Leningrad, VNIMI, 1981 (in Russian).
5. Lavrov, A. The Kaiser effect in rocks: principles and stress estimation techniques. Int. J. Rock Mech. Min. Sci., 2003, 40(2), 151–171. http://www. sciencedirect.com/ science/article/pii/S1365160902001387
https://doi.org/10.1016/S1365-1609(02)00138-7
6. Brown, E. T. Rock Characterization, Testing and Monitoring: I.S.R.M. Suggested Methods. Pergamon Press, 1981.
7. Barr, S. P. The Kaiser Effect of Acoustic Emissions for the Determination of In-Situ Stress in the Carnmenellis Granite. Ph.D. Thesis, University of Exeter, Camborne School of Mines, 1993.
8. Lehtonen, A. Evaluation of Rock Stress Estimation by the Kaiser Effect. Working Report 2005-67, Posiva Oy, Olkiluoto, 2005.
9. Hunt, S. P., Meyers, A. G., Louchnikov, V. Modelling the Kaiser effect and deformation rate analysis in sandstone using the discrete element method. Computers and Geotechnics, 2003, 30(7), 611–621.
https://doi.org/10.1016/S0266-352X(03)00061-2
10. Fairhurst, C. E., Hudson, J. A. Draft ISRM suggested method for the complete stress‑strain curve for intact rock in uniaxial compression. Int. J. Rock Mech. Min. Sci., 1999, 36(3), 279–289.
11. Pollock, A. A., Acoustic emission inspection. In: Metals Handbook, Ninth edition, vol. 17, ASM International, 1989, 278–294.
12. Szwedzicki, T. A hypothesis on modes of failure of rock samples tested in uniaxial compression. Rock Mech. Rock Eng., 2007, 40(1), 97–104.
https://doi.org/10.1007/s00603-006-0096-5
13. Li, C. Deformation and Failure of Brittle Rocks under Compression. Ph.D. Thesis, Luleå University of Technology, Division of Rock Mechanics, 1993.
14. Sabanov, S. Risk Assessment Methods in Estonian Oil Shale Mining Industry. Ph.D. Thesis, Tallinn University of Technology, Mining Department, 2008.
