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Rock Engineering for a Megaton Detector

Rock Engineering for a Megaton Detector. Charles Nelson CNA Consulting Engineers. Overview. Rock engineering 101 Cavern size & shape Construction methods Feasibility Historical projects Numerical modeling Empirical design Other considerations. Rock Engineering 101.

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Rock Engineering for a Megaton Detector

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  1. Rock Engineeringfor aMegaton Detector Charles Nelson CNA Consulting Engineers

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

  3. 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 CNA Consulting Engineers

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

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

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

  7. 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 CNA Consulting Engineers

  8. 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 CNA Consulting Engineers

  9. Cavern size & shape CNA Consulting Engineers

  10. Cavern Size & Shape CNA Consulting Engineers

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

  12. Is a 106 m3 Cavern Feasible? • Previous cavern projects • Numerical modeling • Empirical design methods CNA Consulting Engineers

  13. Is a 106 m3 Cavern Feasible? CNA Consulting Engineers

  14. Numerical Modeling CNA Consulting Engineers

  15. Failure Zones, Cylindrical Cavern Strong Intermediate Weak CNA Consulting Engineers

  16. Failure Zones, Straight Cavern Strong Intermediate Weak CNA Consulting Engineers

  17. 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 CNA Consulting Engineers

  18. 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 CNA Consulting Engineers

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

  20. Rock Quality CNA Consulting Engineers

  21. Rock Quality CNA Consulting Engineers

  22. Rock Quality CNA Consulting Engineers

  23. 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 CNA Consulting Engineers

  24. Rockbolt Length vs Cavern Span CNA Consulting Engineers

  25. Rockbolt Spacing vs Rock Quality CNA Consulting Engineers

  26. Shotcrete Thickness vs Rock Quality CNA Consulting Engineers

  27. Cost Categories CNA Consulting Engineers

  28. 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) CNA Consulting Engineers

  29. 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 CNA Consulting Engineers

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

  31. Common Facilities CNA Consulting Engineers

  32. 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 CNA Consulting Engineers

  33. 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? CNA Consulting Engineers

  34. 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 CNA Consulting Engineers

  35. Compact Layout CNA Consulting Engineers

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

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

  38. Cavern Shapes CNA Consulting Engineers

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

  40. 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? CNA Consulting Engineers

  41. 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 CNA Consulting Engineers

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

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

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

  45. 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 CNA Consulting Engineers

  46. 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 CNA Consulting Engineers

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

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

  49. Salt Cavern CNA Consulting Engineers

  50. Hard Rock Cavern CNA Consulting Engineers

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