Paper contribution

Laboratory Assessment of Shear Strength Parameters of Carpathian Flysch

Andrzej Gluchowski; Wojciech Sas

Proceedings
EUROCK 2026
Pages
1195-1200
Submitted
2 June 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

Carpathian Flysch is a complex sedimentary formation developed as a result of turbidite deposition in a deep-marine basin during the Cretaceous to Miocene period. The sequence consists of rhythmically alternating layers of sandstones, siltstones, mudstones, and shales, formed through successive gravity-driven sediment flows. This characteristic lithological alternation, combined with well-developed foliation and tectonic history of the Carpathian orogen, results in strongly anisotropic mechanical properties of the rock mass. The anisotropy manifests itself in directional variability of stiffness, strength, and deformability, making standard geomechanical characterization particularly challenging. Reliable determination of shear strength parameters of Carpathian Flysch requires careful consideration of sample preparation procedures. Laboratory-prepared reconstituted specimens, commonly used as a cost-effective alternative, fail to preserve the natural fabric, micro-structural discontinuities, and bedding orientation inherent to the intact rock. As a result, triaxial compression tests performed on such specimens systematically overestimate cohesion and misrepresent the friction angle, leading to unconservative geotechnical designs. In contrast, core-derived specimens retain the original structural features of the rock, providing more representative and reliable strength parameters for engineering practice. This study presents a comparative analysis of triaxial test results obtained from reconstituted laboratory specimens and undisturbed core-derived samples of Carpathian Flysch. The experimental program highlights systematic differences in shear strength envelopes between the two specimen types. The findings demonstrate that core-derived specimens should be considered a standard requirement for triaxial testing of anisotropic flysch formations, and that the use of reconstituted samples may introduce significant errors in geomechanical characterization. Practical recommendations for sample preparation and testing procedures are discussed.

Contributors

Authors

  1. Andrzej Gluchowski Warsaw Univrsity of Life Sciences, Poland ORCID 0000-0001-6651-6737
  2. Wojciech Sas Warsaw Univrsity of Life Sciences, Poland

Index terms

Keywords

Full text

Attachments

Works cited

References

  1. Roure, F., Roca, E., & Sassi, W. (1993). The Neogene evolution of the outer Carpathian flysch units (Poland, Ukraine and Romania): kinematics of a foreland/fold-and-thrust belt system. Sedimentary Geology, 86(1-2), 177-201.
  2. Leszczyński, S., Dziadzio, P. S. & Nemec, W., 2015. Some current sedimentological controversies in the Polish Carpathian flysch. In: G. Haczewski (ed.) Guidebook for field trips accompanying 31st IAS Meeting of Sedimentology held in Kraków on 22nd–25th of June 2015. PolishGeologicalSociety, Kraków, pp. 247–287.
  3. Filipek, A., Barski, M., Wysocka, A., & Jankowski, L. (2025). Palynofacies Analysis Illustrates the Source Rock Potential of the Menilite Beds, Polish Outer Carpathians. Journal of Petroleum Geology, 48(4), 352-391.
  4. Murovskaya, A., Hnylko, O., Makarenko, I., Savchenko, O., Kitchka, A., Verpakhovska, O., &Legostaeva, O. (2026). Review and updates of the lithosphere structure and geodynamics evolution of the Neogene Transcarpathian Basin and its substratum (Ukraine). Geological Society, London, Special Publications, 554(1), SP554-2024.
  5. Mihu-Pintilie, A., Dufresne, A., Wolfert, T., &Stoleriu, C. C. (2026). Landslide dam activity in Flysch Zone of the Eastern Carpathian, Romania: distribution, stability, and failure mechanism assessment. Landslides, 1-21.
  6. Roguska, E., & Russo, R. (2025). Tunnel portal design in the demanding geotechnical conditions of Carpathian Flysch. In Tunnelling into a Sustainable Future–Methods and Technologies (pp. 3549-3556). CRC Press.
  7. Bestyński, Z., Sieinski, E., &Śliwiński, P. (2022). Geophysical investigation and the use of their results in the evaluation of the stability of slopes of artificial water reservoirs in the flysch Carpathians. Archives of Civil Engineering, 71-85.
  8. Garzón-Roca, J., Torrijo, F. J., Rodríguez-Peces, M. J., & Ramos, A. (2025). Geological Strength Index quantitative estimation of flysch rock masses from on-field geomechanical data based on AI tools. Bulletin of Engineering Geology and the Environment, 84(6), 348.
  9. Durmeková, T., Bednarik, M., Dikejová, P., & Adamcová, R. (2022). Influence of specimen size and shape on the uniaxial compressive strength values of selected Western Carpathians rocks. Environmental Earth Sciences, 81(9), 247.
  10. Rembiś, M., &Czurczak, J. (2026). Właściwości fizyczno-mechaniczne zróżnicowanych litologicznie skał fliszu karpackiego jako element oceny masywu skalnego na potrzeby budowy tuneli. Przegląd Geologiczny, 74(1).
  11. Zhang, J., Xiang, X., Du, R., &Zhang, X. (2024). Enhancing tunnel stability under high ground stress: rheological analysis and support strategies. Geotechnical and Geological Engineering, 42(5), 3287-3306.
  12. Li, D., Zhou, A., Wang, L., Chen, Y., & Ma, C. (2022). Strength Characteristics and In Situ Stress Measurement of Rock Cores from a Large Section Underground Station: A Case Study. Applied Sciences, 12(21), 10873.
  13. Comegna, L., Mandolini, A., Manna, D., Rianna, G., & Reder, A. (2024). Failure mechanism in a highway embankment founded on a sloping tectonised flysch formation. Procedia Structural Integrity, 62, 484-491.
  14. Ghourtlar, N. S. (2025). Theoretical and experimental investigation of the rock fracture mechanics, focusing on the failure criteria on the intact rock. PhD Thesis, Budapest University of Technology and Economics, Budapest, June 2025.
  15. Berisavljević, Z., Berisavljević, D., & Čebašek, V. (2015). Shear strength properties of Dimitrovgrad flysch, Southeastern Serbia. Bulletin of Engineering Geology and the Environment, 74(3), 759-773.
  16. Łukaszewski, P. (2008). Behaviour of flysch sandstones under conventional triaxial compression. Geologija, 50, Supplement. 131–136