Transcript Rock Mechanics/Seismology - Virginia Tech Department of

Rock Mechanics/Geophysics
Larry Costin, Sandia National Labs
Paul Young, University of Toronto
Discussion Points
DUSEL Workshop
November 12, 2004
We are here
Path Forward
• Identify the “big questions” that can be addressed
by DUSEL in a unique way
• Develop a “roadmap” for evolution of experiments
& facilities
• Define infrastructure requirements
• Integrate with other groups to identify experiment
sets with compatible infrastructure requirements
• Identify significant education outreach
opportunities
Motivation
• Significant trend toward greater utilization of
underground space
–
–
–
–
Critical infrastructure
High hazard facilities
Environmental protection
Urban development
• Current engineering practice has heavy reliance on
empirical design rules
–
–
–
–
Influence of discontinuities
Environmental factors
Time-dependent behavior
Lack of characterization methods for spatial variability
• Few opportunities for long-term R&D efforts
The Big Questions?
• Long-term degradation processes – physical, chemical,
coupled – leading to weakening, rock fall, collapse over
many years.
• Effect of spatial variability of rock mass properties on in
situ stresses and stability of openings.
• Characterizing spatial variability. Validation of methods.
• Measurement of in situ stresses.
• TMHC(B) coupled processes and model validation.
• Validation of mechanics concepts – DEM methods.
• Geophysical imaging and/or characterization of
discontinuities and other features affecting rock mass
behavior.
• Data fusion – can we improve detection and
characterization with data from multiple sensor types?
Unique Opportunities?
• Ability to mine through – ground truth
validation of measurement and
characterization methods.
• Long-term access for science. Ability to
make measurements/observations over
many years.
• Deep earth geophysics observatory.
• International collaboration.
URL Experience
• Excavation scale testing for numerical model
validation – Mine-by Experiment
• Tunnel Sealing eXperiments to simulate
radioactive waste repository conditions –TSX
• Seismic methods used for remote detection and
quantification of damage
Monitoring and Modelling Results: URL Mine-by
PFC
simulation
Excavation
damage
Potyondy and
Cundall, 2001
Recorded seismicity
PFC synthetic
seismicity
48 days
Hazzard et al, 2000
0
Moment
magnitude
-2.2
-3.7
URL Tunnel Sealing Experiment (TSX)
• Phases: Excavation (1997/98); Pressurisation (1999/02);
Heating (2003); Cooling and Depressurisation (2004).
• Scale: Seal 20m x 4.4m x 3.5m
URL TSX Induced Seismicity (1997 – 2003) – Response to
Excavation, Pressurization, and Heating
A : Tunnel Excavation
•
95% of the events occur within 1.4m of the
chamber wall.
•
Events during heating do not extend
further than during excavation
Distance to Chamber Wall (m)
3
A
B
C
D
B : Bulkhead Key Excavation
E
F
C : Bulkhead Seal Construction
2
1
D : Chamber Fill and Pressurization to
2MPa
0
29/08/03
10/02/03
25/07/02
06/01/02
20/06/01
02/12/00
16/05/00
29/10/99
12/04/99
24/09/98
08/03/98
20/08/97
01/02/97
•
High rate of MS activity during excavation.
•
Decay of MS events with pressurisation.
•
Increase around chamber again, especially
in the roof, during heating.
E : Chamber Pressurization to 4MPa
F : Chamber Heating to 80°C
-100
-80
-100
0.5
-0.5
-120
-120
Raypath
P6_R13
-1.5
-140
-2.5
-160
-140
-180
-200
-160
22/08/2003
1.5
23/05/2003
-80
21/02/2003
-60
22/11/2002
-20
23/08/2002
-60
% Change in Youngs Modulus
22/08/2003
23/05/2003
21/02/2003
22/11/2002
23/08/2002
24/05/2002
22/02/2002
23/11/2001
24/08/2001
40
Raypath P4_R8
20
0
1.5
0
-20
-40
-60
20
4.5
0
3.5
-20
-40
2.5
4.5
3.5
1.5
2.5
0.5
-0.5
-1.5
-3.5
-2.5
-4.5
Raypath P6_R13
-4.5
-200
-5.5
% Change in Youngs Modulus
60
% Change in Youngs Modulus
Clay Key Excavation
25/05/2001
23/02/2001
Sand in Chamber
24/05/2002
22/08/2003
23/05/2003
20
22/02/2002
23/11/2001
21/02/2003
22/11/2002
24/11/2000
25/08/2000
26/05/2000
25/02/2000
26/11/1999
27/08/1999
Vs
24/08/2001
25/05/2001
23/08/2002
Water in Chamber
23/02/2001
24/05/2002
22/02/2002
23/11/2001
24/08/2001
25/05/2001
23/02/2001
24/11/2000
Clay Bulkhead Built
24/11/2000
25/08/2000
26/05/2000
25/02/2000
26/11/1999
28/05/1999
26/02/1999
27/11/1998
28/08/1998
29/05/1998
27/02/1998
28/11/1997
29/08/1997
E
25/08/2000
26/05/2000
25/02/2000
26/11/1999
27/08/1999
28/05/1999
26/02/1999
27/11/1998
28/08/1998
29/05/1998
30/05/1997
Vp
27/08/1999
28/05/1999
26/02/1999
27/11/1998
28/08/1998
29/05/1998
27/02/1998
-180
28/11/1997
P6
27/02/1998
R13
-40
28/11/1997
NE
0
29/08/1997
R8
30/05/1997
SW
Velocity Change (m/s)
P4
29/08/1997
NE
Velocity Change
(m/s)
Velocity
Change
(m/s)
SW
30/05/1997
URL TSX Seismic Velocity Measurements 1997-2003:
Temporal Changes to Rock Properties
4.5
3
-1.5
•
•
•
•
•
•
•
-5.5
-3.5
•
Raypath P4_R8
Increase during
excavation.
Decrease during
pressurization.
Large increase during
heating.
-3
Temperature Increase
Pressure Increase
Raypath P6_R13
Large decrease as clay key
excavated and bulkhead
built.
Peaks due to evaporation
experiment.
Increase during heating.
How do Earthquakes Scale?
URL AE
URL MS
(Mw~-7 to -5) (Mw~-4 to -1)
Stress Drop
(from McGarr, 1999)
Mw = -4
Moment Magnitude
Mw = 8
Some questions left unanswered
• Can we use geophysical techniques to
estimate permeability?
• How do we predict and validate the long
term strength and behaviour of fractured
rock?
• How do earthquake processes scale?