Paper contribution

Field Observations and Numerical Back-Analysis of an Excavation in Marl Rock Supported by a Strut-Free Buttress Pile Wall

Timur Grubić; Adis Skejić; Mladen Kapor; Anis Balić

Proceedings
EUROCK 2026
Pages
1175-1180
Submitted
28 January 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

Marl, a transitional soft rock, exhibits complex geotechnical behavior due to its heterogeneous structure, parallel fissures, and variable cementation. The difficulty of obtaining undisturbed samples suitable for laboratory testing makes field-based calibration essential for realistic modeling of excavation performance. This paper presents field observations and numerical back-analysis of a strut-free excavation in marl rock supported by buttress pile walls. The study aims to calibrate the stiffness parameters of the Hardening Soil (HS) model to accurately reproduce the deformation behavior of the marl under actual excavation conditions. Field observations and a monitoring program, including systematic inclinometer measurements, were implemented to provide reliable reference data for model calibration and validation. The excavation was almost entirely in marl, ensuring consistent geotechnical conditions and eliminating the influence of other soil or rock layers that often complicate similar case studies. A three-dimensional finite-element back-analysis was conducted to evaluate the deformation behavior of the self-supporting buttress pile wall during staged excavation and to determine the stiffness parameters that best reproduce the observed field performance. Since both shear strength and stiffness govern wall displacements, shear strength values were fixed based on independent large-scale direct shear tests on intact marl and discontinuity samples from previous studies. Consequently, the analysis focused on identifying stiffness characteristics representative of marl rock under real excavation conditions. The calibrated parameters successfully captured the observed wall and ground deformations, providing a realistic representation of the excavation behavior. The findings offer valuable guidance for similar engineering problems, supporting more reliable prediction of system response in weak and transitional marl formations. Moreover, the results contribute to improved risk management and more informed geotechnical design decisions in future excavation projects under comparable geological and structural conditions.

Contributors

Authors

  1. Timur Grubić University of Sarajevo - Faculty of Civil Engineering
  2. Adis Skejić University of Sarajevo - Faculty of Civil Engineering ORCID 0000-0001-8699-9430
  3. Mladen Kapor University of Sarajevo - Faculty of Civil Engineering
  4. Anis Balić University of Sarajevo - Faculty of Civil Engineering

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References

  1. Berisavljević, D., Berisavljević, Z., Melentijević, S. (2022). The shear strength evaluation of rough and infilled joints and its indications for stability of rock cutting in schist rock mass. Bulletin of Engineering Geology and the Environment, 81(3), 113. https://doi.org/10.1007/s10064-022-02580-8.
  2. Son, M., Park,J. (2014). Physical and numerical tests of the excavation walls in jointed rock masses. Canadian Geotechnical Journal. 51(5): 554-569. https://doi.org/10.1139/cgj-2013-0081.
  3. Grubić T, Skejić A., Kapor M, Balić A (2025). Effectiveness of the Outer Buttress Walls in Minimizing Displacements of Strut-Free Excavation: Physical and Numerical Modeling. Indian Geotech J 56, 1328–1345 https://doi.org/10.1007/s40098-025-01227-1.
  4. Lim A, Ou C.Y., Hsieh P.G. (2017). Investigation of the integrated retaining system to limit deformations induced by deep excavation. Acta Geotech 13(4):973–995. https:// doi. org/ 10. 1007/s11440-017-0613-6.
  5. Alpan, I. (1970).The geotehnical properties of soil. Eart-Science Reviews, 6:5-49.
  6. ISRM Turkish National Group: The complete ISRM Suggested methods for Rock Characterization, Testing and Monitoring: 1974 - 2006. Ulusay, R., Hudson J.A. (Editors). Ankara, Turkey, 2007.
  7. Strugar N. (1985) Otpornost na smicanje nekih kategorija “mekanih” stijena. Sarajevo (Bosnia and Herzegovina)
  8. Brinkgreve R.B.J., Kumarswamy S., Swolfs W.M. (2015). Plaxis 3D anniversary edition manual. Delft University of Technology and Plaxis BV, Netherlands.
  9. Skejić, A., Balić, A., Kapor, M. (2023). Case history on excessively large displacements and remediation of pile-supported excavation in a sloping ground. Engineering Failure Analysis, 143, 106856.https://doi.org/10.1016/j.engfailanal.2022.106856.
  10. Bajramović, N., Skejić, A. (2025). Structural Failure of Strutted Soldier Pile Wall: Emergency Response, Forensic Diagnosis, and Postaccident Remediation. Indian Geotechnical Journal, 1-21.https://doi.org/10.1007/s40098-025-01433-x.
  11. Yue, J., Wang, D., Jiang, Y., Shi, S., Huang, Y. (2024). Determination of Shear Strength Parameters of Concrete Materials Based on the Rectangular Section Splitting Method. Materials, 17(24), 6141. https://doi.org/10.3390/ma17246141.
  12. Lelović, S.,Vasović, D. (2020). Determination of Mohr-Coulomb Parameters for Modelling of Concrete. Crystals, 10(9), 808. https://doi.org/10.3390/cryst10090808.
  13. Schanz T, Vermeer P.A., Bonnier P.G. (1999). The hardening soil model: formulation and verification. Comput Geotech 281–296.