1. REFLECTIONS ON 30 YEARS IN GROUND CONTROL

2. Analysis of Retreat Mining Pillar Stability (ARMPS): Version 6 (2010) 6 2010

4. LsLs D C A WsWs c4c1 c2 c3 LbLb

6. We could spend a million dollars trying to explain why this intersection collapsed…

7. But then how do we explain the 100 nearby “just like it” that stayed up??!!

8. Other engineers have accurate knowledge of material properties and applied loads.

9. Because rock mass behavior is so complex, we need a different approach.

10. From a practical standpoint, maybe its “good enough” to know that the odds of failure were 1-in-100.

11. Make use of knowledge gained during “full scale testing” of mine designs. EMPIRICAL METHODS

12. Empirical methods focus on the success or failure of the full scale design.

13. Require a simplified model that includes all the important factors.

15. TAILGATE ENTRY STABILITY

17. Empirical design guidelines are closely linked to reality, easy to understand, and easy to use.

18. Analysis of Retreat Mining Pillar Stability (ARMPS) Analysis of Multiple Seam Stability (AMSS)

19. SYNERGY WITH NUMERICAL MODELS

20. Safety During Pillar Recovery: A Ground Control Success Story

22. Fatal Roof Falls During Retreat Mining 1995-2005

23. Fatal Roof Falls During Retreat Mining 1995-2011 One fatal roof fall in six years

24. Leave the final stump Use extra roof bolt support Mobile Roof Supports Technologies that made the difference

25. Retreat Mining ~ 30 million tons/year ~ 400 tons/pillar ~ 80,000 pillars/year ~ 200 retreat mines ~ 400 pillars/mine/year

26. Retreat Mining ~ 80,000 pillars/year ~ 400 pillars/mine/year Prior to 2005, nationwide there were ~ 2 fatals/year ~ Rate was 1 fatal/40,000 pillars Typical mine: One fatal every 100 years

27. CRANDALL CANYON MINE DISASTER