Paper contribution

Deterministic DFN Modelling and Analysis of Large Caverns at 1000 m Depth

Ali Rahnama; David Saiang

Proceedings
EUROCK 2026
Pages
1001-1008
Submitted
28 January 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

Hoek and Brown (1980) and Brady and Brown (2006) classify underground excavations into four span categories: (i) normal (5–10 m), (ii) wide (10–20 m), (iii) very wide (20–30 m), and (iv) ultra-wide (>30 m). A practical cut-off for wide-span excavations is generally taken as 10–15 m. Normal spans encompass most transportation tunnels, while subway stations and underground parking facilities fall within the wide-span range. Very-wide and ultra-wide spans include hydropower machine halls, large mining chambers, underground research laboratories, and specialized underground sports and storage halls. The importance of wide to ultra-wide underground spaces continues to increase as the demand for infrastructure rises and surface space becomes increasingly constrained. Underground siting provides a sustainable alternative that minimizes surface disturbance and offers a stable, isolated environment advantageous for many scientific applications. As spans increase, the mechanical behaviour of the surrounding rock mass departs significantly from that of normal-span tunnels. Larger spans create extensive stress-disturbed zones with low confinement, promoting brittle fracture processes, strain localization, and, at greater depths, the potential for rock-bursting. A central challenge is to evaluate rock-mass response under high in-situ stresses and to ensure that support systems can accommodate both immediate and long-term deformation. These excavations therefore require advanced analyses to assess their stability, safety, and performance over their service life. This paper investigates the stability of two super-large, dome-shaped underground caverns with unprecedented ultra-wide dimensions of 75 m diameter, located approximately 1000 m below surface to meet stringent scientific requirements. A distinct-element numerical model was developed to examine their stability. To better understand key risks, representative joint systems were incorporated, and sensitivity analyses were performed on joint spacing and persistence. The performance of a primary support system—comprising rock bolts, pretensioned cable bolts, and shotcrete—was evaluated to assess the interaction between reinforcement and the jointed rock mass.

Contributors

Authors

  1. Ali Rahnama Lulea university of technology, Sweden ORCID 0009-0005-3285-4806
  2. David Saiang Lulea university of technology, Sweden

Index terms

Keywords

Full text

Attachments

Works cited

References

  1. Barton N, Choubey V (1977) The shear strength of rock joints in theory and practice. Rock Mechanics 10:1–54.
  2. Barton N, Lien R, Lunde J (1974) Engineering classification of rock masses for the design of tunnel support. Rock Mechanics 6:189–236.
  3. Brady BHG, Brown ET (2004) Rock mechanics for underground mining. 3rd edn. Springer, Dordrecht.
  4. Cao R, Dai H, Yao R, Lin H, Li K (2022) Failure behaviour of jointed rock masses with 3D nonpenetrating joints under uniaxial compression: Insights from discrete element method modelling. Applied Sciences 12:11027.
  5. Cundall PA, Pierce ME, Mas Ivars D (2008) Quantifying the size effect of rock mass strength. First Southern Hemisphere International Rock Mechanics Symposium (SHIRMS 2008), Perth, Australia.
  6. Daffern T, Ellis R, King P, Richardson S, Glücksman E, Beveridge A (2017) NI 43-101 technical report for the Zinkgruvan Mine, Sweden. Lundin Mining Corporation.
  7. Dershowitz WS, Herda HH (1992) Interpretation of fracture spacing and intensity. 33rd U.S. Symposium on Rock Mechanics, Santa Fe, New Mexico.
  8. Diederichs MS (2007) The 2003 Canadian Geotechnical Colloquium: Mechanistic interpretation and practical application of damage and spalling prediction criteria for deep tunnelling. Canadian Geotechnical Journal 44(9):1082–1116.
  9. Goodman RE, Shi GH (1985) Block theory and its application to rock engineering. Prentice-Hall, Englewood Cliffs.
  10. Hoek E, Brown ET (1980) Underground excavations in rock. Institution of Mining and Metallurgy, London.
  11. Lei Q, Latham JP, Tsang CF (2017) The use of discrete fracture networks for modelling coupled geomechanical and hydrological behaviour of fractured rocks. Computers and Geotechnics 85:151–176.
  12. Lindblom U, Ericsson LO, Winqvist T, Tengborg P, Håkansson U (eds) (2018) Sweden underground: Rock engineering and how it benefits society. BeFo Rock Engineering Research Foundation and Swedish Rock Engineering Association, Stockholm.
  13. Montano Atencio JA (2024) Stability analysis on the proposed excavation ESSνSB caverns. Master’s thesis, New Mexico Institute of Mining and Technology.
  14. Oda M (1988) A method for evaluating the representative elementary volume based on joint survey of rock masses. Canadian Geotechnical Journal 25(3):440–447.
  15. Rahnama A, Saiang D, Montano Atencio JA (2025) Stability analysis of large underground caverns of unprecedented dimensions at depth. 59th U.S. Rock Mechanics/Geomechanics Symposium, Santa Fe, New Mexico, USA.
  16. Saiang D (2019) Pre-study of candidate site for underground infrastructure for neutrino research. UNRI project report. Luleå University of Technology, Luleå.
  17. Shang J, West LJ, Hencher SR, Zhao Z (2018) Geological discontinuity persistence: Implications and quantification. Engineering Geology 241:41–54.
  18. Wei S, Li Y, Shang Y, Sun Y, Li K (2022) Stability analysis of fractured rock mass around underground excavations based on a three-dimensional discrete fracture network. Environmental Earth Sciences 81:65.