January 2002 - Cern

frizzflowerUrban and Civil

Nov 29, 2013 (3 years and 10 months ago)

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Rock Engineering

for 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

Cylinder
Torus
Straight
SuperK
Soudan 2
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 10
6

m
3

Cavern Feasible?


Previous cavern projects


Numerical modeling


Empirical design methods

January 2002

CNA Consulting Engineers

Is a 10
6

m
3

Cavern Feasible?

0
200,000
400,000
600,000
800,000
1,000,000
0
20
40
60
80
100
120
Span (m)
Volume (cubic meters)
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)
Rockbolt Length (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
Rockbolt Spacing (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
Shotcrete Thickness (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