Post on 19-Dec-2015
Rock Engineeringfor a
Megaton Detector
Charles Nelson
CNA Consulting Engineers
January 2002 CNA Consulting Engineers
Overview
• Rock engineering 101• Cavern size & shape• Construction methods• Feasibility
– Historical projects– Numerical modeling– Empirical design
• Other considerations
January 2002 CNA 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
January 2002 CNA Consulting Engineers
Rock Engineering 101
• Massive rock– Rock masses with few
discontinuities, or– Excavation dimension
< discontinuity spacing
January 2002 CNA Consulting Engineers
Rock Engineering 101
• Jointed or “blocky” rock– Rock masses with
moderate number of discontinuities
– Excavation dimension > discontinuity spacing
January 2002 CNA Consulting Engineers
Rock Engineering 101
• Heavily jointed rock– Rock masses with a
large number of discontinuities
– Excavation dimension >> discontinuity spacing
January 2002 CNA 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
January 2002 CNA 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
January 2002 CNA Consulting Engineers
Cavern size & shape
January 2002 CNA Consulting Engineers
Cavern Size & Shape
January 2002 CNA Consulting Engineers
Construction methods
• Drill & blast
• Small top headings
• Install rock support
• Large benches
January 2002 CNA Consulting Engineers
Is a 106 m3 Cavern Feasible?
• Previous cavern projects
• Numerical modeling
• Empirical design methods
January 2002 CNA Consulting Engineers
Is a 106 m3 Cavern Feasible?
0
200,000
400,000
600,000
800,000
1,000,000
0 20 40 60 80 100 120Span (m)
Vo
lum
e (
cu
bic
me
ters
)
Existing NG Caverns
January 2002 CNA Consulting Engineers
Numerical Modeling
January 2002 CNA Consulting Engineers
Failure Zones, Cylindrical Cavern
Strong Intermediate Weak
January 2002 CNA Consulting Engineers
Failure Zones, Straight Cavern
Strong Intermediate Weak
January 2002 CNA 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
January 2002 CNA 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
January 2002 CNA Consulting Engineers
Rock Quality
Q=100 Q=3 Q=0.1
January 2002 CNA Consulting Engineers
Rock Quality
January 2002 CNA Consulting Engineers
Rock Quality
January 2002 CNA Consulting Engineers
Rock Quality
January 2002 CNA 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
January 2002 CNA Consulting Engineers
Rockbolt Length vs Cavern Span
0
5
10
15
20
0 20 40 60 80 100
Cavern Span (m)
Ro
ck
bo
lt L
en
gth
(m
)
Empirical Data Cavern Spans
January 2002 CNA Consulting Engineers
Rockbolt Spacing vs Rock Quality
0
1
2
3
0.01 0.1 1 10 100
NGI "Q" Rating
Ro
ckb
olt
Sp
acin
g (
m)
Empirical Values Examples
January 2002 CNA Consulting Engineers
Shotcrete Thickness vs Rock Quality
0
100
200
300
400
0.01 0.1 1 10 100
NGI "Q" Rating
Sh
otc
rete
Th
ickn
ess
(mm
)
Empirical Values Examples
January 2002 CNA Consulting Engineers
Cost Categories
Excavation
Haulage
Support
Access Tunnel
Ancillary Space
Mobilization,Bond, etc.
Permits, Fees,Eng, etc.
January 2002 CNA 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)
January 2002 CNA 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
January 2002 CNA Consulting Engineers
U.G. Space Considerations
• Common facilities (infrastructure & usable space)
• Cavern shapes & sizes
• Laboratory-experiment relationship
• Special needs
January 2002 CNA Consulting Engineers
Common Facilities
January 2002 CNA 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
January 2002 CNA 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?
January 2002 CNA 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
January 2002 CNA Consulting Engineers
Compact Layout
January 2002 CNA 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
January 2002 CNA Consulting Engineers
Cavern Shapes
• Use simple shapes, e.g. rural mailbox• Avoid inside corners• Avoid tall, narrow shapes• Roof costs the most
January 2002 CNA Consulting Engineers
Cavern Shapes
January 2002 CNA Consulting Engineers
Cavern Shapes
• Avoid complex intersections
• Avoid closely spaced, parallel excavations
• Overexcavation & underexcavation are common
January 2002 CNA 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?
January 2002 CNA 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
January 2002 CNA Consulting Engineers
Other Experience
• Kansas City, MO, converted limestone mines widely used for warehouse & manufacturing
January 2002 CNA Consulting Engineers
Underground Owners:
• Interact with building code officials
• Prepare & enforce design / construction standards
• Control tenant improvements
• Control occupancy
• Restrict structural modifications
January 2002 CNA Consulting Engineers
Underground Owners:
• Restrict chemicals & hazardous materials
• Require regular maintenance
• Provide labor or preferred contractors for improvements
• Typically make all improvements
January 2002 CNA 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
January 2002 CNA 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
January 2002 CNA Consulting Engineers
Special Needs
• Shape
• Shielding
• Clean rooms, clean lab?
• Radon control
• Magnetic field cancellation
• Power use or reliability
• Heat generation
January 2002 CNA Consulting Engineers
Special Needs (cont.)
• Water supply
• Flammable detector materials/gasses
• Suffocating gasses
• Occupancy
• Hours of access
January 2002 CNA Consulting Engineers
Salt Cavern
January 2002 CNA Consulting Engineers
Hard Rock Cavern
January 2002 CNA Consulting Engineers