1. Rock Engineering for a Megaton Detector Charles Nelson CNA Consulting Engineers

2. January 2002CNA Consulting Engineers Overview Rock engineering 101 Cavern size & shape Construction methods Feasibility –Historical projects –Numerical modeling –Empirical design Other considerations

3. January 2002CNA Consulting Engineers Rock Engineering 101 Rock “material” — strong, stiff, brittle –Weak rock > Strong concrete –Strong in compression, weak in tension –Postpeak strength is low unless confined Rock “mass” — behavior controlled by discontinuities –Rock mass strength is 1/2 to 1/10 of rock material strength Discontinuities give rock masses scale effects

4. January 2002CNA Consulting Engineers Rock Engineering 101 Massive rock –Rock masses with few discontinuities, or –Excavation dimension < discontinuity spacing

5. January 2002CNA Consulting Engineers Rock Engineering 101 Jointed or “blocky” rock –Rock masses with moderate number of discontinuities –Excavation dimension > discontinuity spacing

6. January 2002CNA Consulting Engineers Rock Engineering 101 Heavily jointed rock –Rock masses with a large number of discontinuities –Excavation dimension >> discontinuity spacing

7. January 2002CNA Consulting Engineers Rock Engineering 101 Rock stresses in situ –Vertical stress  weight of overlying rock –~27 Kpa / m  16.5 MPa at 610 m –~1.2 psi / ft  2,400 psi at 2000 ft –Horizontal stress controlled by tectonic forces (builds stresses) & creep (relaxes stresses) –At depth,  v   h unless there are active tectonic forces

8. January 2002CNA Consulting Engineers Rock Engineering 101 What are the implications for large cavern construction? –Find a site with good rock –Characterizing the rock mass is JOB ONE –Avoid tectonic zones & characterize in situ stresses –Select size, shape & orientation to minimize zones of compressive failure or tensile stress

9. January 2002CNA Consulting Engineers Cavern size & shape

10. January 2002CNA Consulting Engineers Cavern Size & Shape

11. January 2002CNA Consulting Engineers Construction methods Drill & blast Small top headings Install rock support Large benches

12. January 2002CNA Consulting Engineers Is a 10 6 m 3 Cavern Feasible? Previous cavern projects Numerical modeling Empirical design methods

13. January 2002CNA Consulting Engineers Is a 10 6 m 3 Cavern Feasible?

14. January 2002CNA Consulting Engineers Numerical Modeling

15. January 2002CNA Consulting Engineers Failure Zones, Cylindrical Cavern StrongIntermediateWeak

16. January 2002CNA Consulting Engineers Failure Zones, Straight Cavern StrongIntermediateWeak

17. January 2002CNA Consulting Engineers Empirical design methods Appropriate during feasibility assessments Require classification of the rock mass Most commonly used today: –Bieniawski RMR rating –NGI Q rating NGI Q rating used in the following

18. January 2002CNA Consulting Engineers Rock Quality Assumptions Q=100 –One joint set; rough, irregular, undulating joints with tightly healed, hard, non-softening, impermeable filling; dry or minor water inflow; high stress, very tight structure Q=3 –Two joint sets plus misc.; smooth to slickensided, undulating joints; slightly altered joint walls, some silty or sandy clay coatings; medium water inflows, single weakness zones Q=0.1 –Three joint sets; slickensided, planar joints with softening or clay coatings; large water inflows; single weakness zones

19. January 2002CNA Consulting Engineers Rock Quality Q=100 Q=3Q=0.1

20. January 2002CNA Consulting Engineers Rock Quality

21. January 2002CNA Consulting Engineers Rock Quality

22. January 2002CNA Consulting Engineers Rock Quality

23. January 2002CNA Consulting Engineers Rock support methods Rockbolts or cable bolts –Provides tensile strength & confinement Shotcrete –Sprayed on concrete –Provides arch action, prevents loosening, seals Concrete lining –Used when: Required thickness exceeds practical shotcrete thickness Better finish is needed

24. January 2002CNA Consulting Engineers Rockbolt Length vs Cavern Span

25. January 2002CNA Consulting Engineers Rockbolt Spacing vs Rock Quality

26. January 2002CNA Consulting Engineers Shotcrete Thickness vs Rock Quality

27. January 2002CNA Consulting Engineers Cost Categories

28. January 2002CNA Consulting Engineers Cost Conclusions Costs are sensitive to: –volume –rock quality Costs are insensitive to: –Cavern shape Costs are moderately sensitive to: –Horizontal vs. vertical access (within ranges considered)

29. January 2002CNA Consulting Engineers Challenges Find the best possible rock in an acceptable region Find a site with feasible horizontal access Explore co-use opportunities Develop layouts amenable to low cost excavation methods Give Geotechnical considerations as much weight as possible

30. January 2002CNA Consulting Engineers U.G. Space Considerations Common facilities (infrastructure & usable space) Cavern shapes & sizes Laboratory-experiment relationship Special needs

31. January 2002CNA Consulting Engineers Common Facilities

32. January 2002CNA Consulting Engineers Common Facilities What common facilities are beneficial/desirable? –Power, water, sewer, communications –Machine shop, assembly areas?? –Storage, clean rooms?? How should common space be allocated between underground & aboveground? –Administration, storage

33. January 2002CNA Consulting Engineers Common Facilities Radon control –Should the whole lab have radon control or just certain areas? –What is the best means? Sealing? Outside air? Lab cleanliness standards –100? 1,000? 10,000? –What standards for what spaces? –What are the requirements for the various experiments?

34. January 2002CNA Consulting Engineers Compact vs. Open Layout? Compact layout –Allows more interaction –Common space is more usable –Reduced infrastructure costs –Reduced cost to provide multiple egress ways –Preserves underground space

35. January 2002CNA Consulting Engineers Compact Layout

36. January 2002CNA Consulting Engineers Compact vs. Open Layout? Open layout –Better isolation –Reduced impact during expansion Essential to create a Master Plan that will guide lab development

37. January 2002CNA Consulting Engineers Cavern Shapes Use simple shapes, e.g. rural mailbox Avoid inside corners Avoid tall, narrow shapes Roof costs the most

38. January 2002CNA Consulting Engineers Cavern Shapes

39. January 2002CNA Consulting Engineers Cavern Shapes Avoid complex intersections Avoid closely spaced, parallel excavations Overexcavation & underexcavation are common

40. January 2002CNA Consulting Engineers Laboratory-Experiment Issues What are the issues? –Different sources of funding –Shared responsibilities –Shared liabilities –Users/tenants rights –Conflict resolution –Decommissioning (escrow funds?) –Private tenants?

41. January 2002CNA Consulting Engineers Specific examples How many caverns does the lab provide? 0? 1? 2? More? Cavern sharing? –Large caverns are cheaper –Shared caverns create conflicts What is the logical boundary between lab- provided services and experiment-provided services? –Power, heating & cooling, clean rooms –Storage space, assembly space

42. January 2002CNA Consulting Engineers Other Experience Kansas City, MO, converted limestone mines widely used for warehouse & manufacturing

43. January 2002CNA Consulting Engineers Underground Owners: Interact with building code officials Prepare & enforce design / construction standards Control tenant improvements Control occupancy Restrict structural modifications

44. January 2002CNA Consulting Engineers Underground Owners: Restrict chemicals & hazardous materials Require regular maintenance Provide labor or preferred contractors for improvements Typically make all improvements

45. January 2002CNA Consulting Engineers What is not the same? Funding –Typical UG space, tenants pay –For NUSL, lab funding & experiment funding are separate Special needs –Typical UG space, special needs limited –For NUSL, everything is special

46. January 2002CNA Consulting Engineers What is not the same? Common space –Typical UG space, limited common space –For NUSL, extensive common space Shared space –Typical UG space, share only infrastructure –For NUSL, experiments may share caverns

47. January 2002CNA Consulting Engineers Special Needs Shape Shielding Clean rooms, clean lab? Radon control Magnetic field cancellation Power use or reliability Heat generation

48. January 2002CNA Consulting Engineers Special Needs (cont.) Water supply Flammable detector materials/gasses Suffocating gasses Occupancy Hours of access

49. January 2002CNA Consulting Engineers Salt Cavern

50. January 2002CNA Consulting Engineers Hard Rock Cavern

51. January 2002CNA Consulting Engineers