Rock engineering for a megaton detector
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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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Rock engineering for a megaton detector

Rock Engineeringfor aMegaton Detector

Charles Nelson

CNA Consulting Engineers


Overview

Overview

  • Rock engineering 101

  • Cavern size & shape

  • Construction methods

  • Feasibility

    • Historical projects

    • Numerical modeling

    • Empirical design

  • Other considerations

CNA Consulting Engineers


Rock engineering 101

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

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Rock engineering 1011

Rock Engineering 101

  • Massive rock

    • Rock masses with few discontinuities, or

    • Excavation dimension < discontinuity spacing

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Rock engineering 1012

Rock Engineering 101

  • Jointed or “blocky” rock

    • Rock masses with moderate number of discontinuities

    • Excavation dimension > discontinuity spacing

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Rock engineering 1013

Rock Engineering 101

  • Heavily jointed rock

    • Rock masses with a large number of discontinuities

    • Excavation dimension >> discontinuity spacing

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Rock engineering 1014

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

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Rock engineering 1015

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

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Cavern size shape

Cavern size & shape

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Cavern size shape1

Cavern Size & Shape

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Construction methods

Construction methods

  • Drill & blast

  • Small top headings

  • Install rock support

  • Large benches

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Is a 10 6 m 3 cavern feasible

Is a 106 m3 Cavern Feasible?

  • Previous cavern projects

  • Numerical modeling

  • Empirical design methods

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Is a 10 6 m 3 cavern feasible1

Is a 106 m3 Cavern Feasible?

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Numerical modeling

Numerical Modeling

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Failure zones cylindrical cavern

Failure Zones, Cylindrical Cavern

Strong

Intermediate

Weak

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Failure zones straight cavern

Failure Zones, Straight Cavern

Strong

Intermediate

Weak

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Empirical design methods

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

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Rock quality assumptions

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

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Rock quality

Rock Quality

Q=100

Q=3

Q=0.1

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Rock quality1

Rock Quality

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Rock quality2

Rock Quality

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Rock quality3

Rock Quality

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Rock support methods

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

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Rockbolt length vs cavern span

Rockbolt Length vs Cavern Span

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Rockbolt spacing vs rock quality

Rockbolt Spacing vs Rock Quality

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Shotcrete thickness vs rock quality

Shotcrete Thickness vs Rock Quality

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Cost categories

Cost Categories

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Cost conclusions

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)

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Challenges

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

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U g space considerations

U.G. Space Considerations

  • Common facilities (infrastructure & usable space)

  • Cavern shapes & sizes

  • Laboratory-experiment relationship

  • Special needs

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Common facilities

Common Facilities

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Common facilities1

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

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Common facilities2

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?

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Compact vs open layout

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

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Compact layout

Compact Layout

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Compact vs open layout1

Compact vs. Open Layout?

  • Open layout

    • Better isolation

    • Reduced impact during expansion

  • Essential to create a Master Plan that will guide lab development

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Cavern shapes

Cavern Shapes

  • Use simple shapes, e.g. rural mailbox

  • Avoid inside corners

  • Avoid tall, narrow shapes

  • Roof costs the most

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Cavern shapes1

Cavern Shapes

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Cavern shapes2

Cavern Shapes

  • Avoid complex intersections

  • Avoid closely spaced, parallel excavations

  • Overexcavation & underexcavation are common

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Laboratory experiment issues

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?

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Specific examples

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

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Other experience

Other Experience

  • Kansas City, MO, converted limestone mines widely used for warehouse & manufacturing

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Underground owners

Underground Owners:

  • Interact with building code officials

  • Prepare & enforce design / construction standards

  • Control tenant improvements

  • Control occupancy

  • Restrict structural modifications

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Underground owners1

Underground Owners:

  • Restrict chemicals & hazardous materials

  • Require regular maintenance

  • Provide labor or preferred contractors for improvements

  • Typically make all improvements

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What is not the same

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

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What is not the same1

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

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Special needs

Special Needs

  • Shape

  • Shielding

  • Clean rooms, clean lab?

  • Radon control

  • Magnetic field cancellation

  • Power use or reliability

  • Heat generation

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Special needs cont

Special Needs (cont.)

  • Water supply

  • Flammable detector materials/gasses

  • Suffocating gasses

  • Occupancy

  • Hours of access

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Salt cavern

Salt Cavern

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Hard rock cavern

Hard Rock Cavern

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Rock engineering for a megaton detector

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