Paper contribution

Assessing Caving Risk Related to Rockmass Bulking

Trevor G. Carter; Andre van As

Proceedings
EUROCK 2026
Pages
793-799
Submitted
28 January 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

Establishing how much or how little a rockmass bulks during caving is critical to assessing surface subsidence risk for civil tunnel and near-surface mining stope collapses, and to evaluating cave initiation and draw performance in block and panel cave mines. The volumetric expansion that occurs as a rockmass breaks up determines whether the cave back self-chokes or propagates progressively upward. Bulking depends on rockmass characteristics controlling block size and shape, as well as stress conditions, fall height of detached blocks and the fragmented rock maturity through comminution and compaction. The excavation damage/yield zone geometry, fragmentation rates and stress redistribution further influence how the rock mass breaks and ultimately cave propagation. Insufficient understanding of these interacting processes has historically caused catastrophic tunnel and crown pillar collapses and major cave propagation difficulties in cave mining. This paper reviews empirical methods for evaluating crown collapse risk and caveability, including the scaled-span approach and Laubscher's MRMR hydraulic-radius framework. Particular emphasis is placed on the role of bulking in controlling void ratio, stress transfer and cave propagation. Guidelines for assessing bulking are presented based on precedent case histories, laboratory data and numerical modelling insights.

Contributors

Authors

  1. Trevor G. Carter TGC-Geo-Solutions, Oakville ,Canada ORCID 0000-0001-6746-959X
  2. Andre van As University of Queensland, Brisbane, Australia

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References

  1. Brown, ET., (2003, 2006) Block Caving Geomechanics. JKMRC, Brisbane.
  2. Carter, TG.,(1989). Design Lessons from Evaluation of OldCrown Pillar Failures. Proc. Int. Conference on Surface CrownPillars for Active and Abandoned Metal Mines, Timmins,Canada. pp.177-187.
  3. Carter, TG.,(1992). A New Approach to Surface Crown PillarDesign. Proc. 16th Canadian Rock Mechanics. Symposium, Sudbury, pp. 75-83.
  4. Carter, TG., Alcott, J. &Castro, LM., (2002). ExtendingApplicability of the Crown Pillar Scaled Span Method toShallow Dipping Stopes, Proc. 5th Nth. American Rock Mech.Symp., pp.1049-1059.
  5. Carter, TG., Cottrell, BE., Carvalho, JL. & Steed, CM., (2008) Logistic Regression Improvements to the Scaled Span Method for dimensioning Surface Crown Pillars over Civil or Mining Openings. Proc. 42nd US Rock Mech. Symp. & 2nd Can-US Rock Symp., San Francisco, Paper 08-282. 13pp.
  6. Carter, TG., (2014) Guidelines for use of the Scaled Span Method for Surface Crown Pillar Stability Assessment. Proc. 1st Int. Conf. Applied Empirical Design Methods in Mining, Lima, Peru, 34pp.
  7. Carter, TG., (2019) Retrospective Assessment of Structurally Controlled Crown Pillar Failures Proc. 53rd N. Amer. Rock Mechanics Symposium. New York. Paper ARMA 19-2163 16pp.
  8. Carter, TG. & Miller, RI., (1996) Some Observations on the Time Dependency of Collapse of Surface Crown Pillars. Proc. 2nd N. American Rock Mech. Symp., Montreal, V.1, pp.285-294.
  9. Cuello, D. & Newcombe, G., (2014) Key geotechnical learnings from cave mining. Proc. 3rd Int. Symp. Block and Sublevel Caving, Santiago.
  10. Golder Associates (1990) (Carter, TG., Yuen., CMK.,Barrett., SLV. & Wong, JS.,)Crown Pillar Stability Back-Analysis. Report to Canada Centre for Mineral and Energy Technology, #23440-8-9074/01-SQ, 90pp.
  11. Hoek E. & Brown ET., (1980) Empirical strength criterion for rockmasses. J Geot.Eng 106,GT9: pp.1013-1035
  12. Laubscher, DH., (1977) Geomechanics Classification of Jointed Rock Masses - Mining Applications. Trans. Inst. Min. Metall. (Sect.A) Vol.86, pp. A1-A8.
  13. Laubscher, DH., (1994) Cave mining - the state of the art. J. S. Afr. Inst. Min. Metall., 94(10): pp.279-293.
  14. Laubscher, DH., (2000) A Practical Manual on Block Caving.Report prepared under auspices of International Caving Study(1997-2000) 525pp.
  15. Marinos, VP. & Carter, TG., (2025) Integrating GSI and mi for Reliable Rockmass Strength Estimation. Proc. 1st International Rock Mass Classification Conference; Oslo, Rock Mechanics & Rock Engineering, Issue 10/2025, vol 58: pp.11216-11260; https://doi.org/10.1007/s00603-025-04792-2
  16. Sainsbury, BL., Pierce, ME. & Mas Ivars, D., (2011) Simulation of rock mass strength anisotropy and scale effects using a Ubiquitous Joint Rock Mass (UJRM) model. Proc. 1st Int. FLAC/DEM Symp., Minneapolis.
  17. Sharrock, GB., Cuello, D. & Rojas, E., (2012) Modelling draw in a sublevel cave mine. Proc. 6th Int. Conf. on Mass Mining, Sudbury.
  18. Van As, A & Van Hout, G.,(2008), Implications of widely spaced drawpoints, in H Schunnesson& E Nordlund (eds), MassMin 2008: Proceedings of the Fifth International Conference and Exhibition on Mass Mining, Luleå University of Technology, Luleå.
  19. van As, A & Guest, A., (2020), 'The design & operating philosophies of Panel vs Block Caving', in R Castro, F Báez & K Suzuki (eds), MassMin 2020: Proceedings of the Eighth International Conference & Exhibition on Mass Mining, University of Chile, Santiago, pp. 207-220,