Transcript A Large Block Test

A Large Block Test to Study the Energetic
Failure of Rock –
Application to Rock-Bursting and
Earthquake Mechanics
Maochen Ge, Eliza Richardson, Chris Marone,
Derek Elsworth, EMS, PSU & Erik Westman, VPI
Objectives
• Develop an improved understanding of the
deformation and energetic failure of rock
masses
– Contribute to the safe design of structures
(e.g. infrastructure and caverns)
– Improved understanding of rock failure in
space and time
– Address a “big” question: Rupture mechanics
and AE/MS/RB/Equake scaling
Slide-Hold-Slide Friction Experiments
•Hold periods of 30 – 104 [sec]
0.75
0.70
30 s
0.65
100 s
300 s
1000 s
0.60
3000 s
10000 s
o
T = 20 C
0.55
10.0
10.5
11.0
11.5
12.0
12.5
Shear displacement [mm]
13.0
Coefficient of friction
Coefficient of friction
0.75
0.70
0.65
30 s
0.60
100 s
300 s
0.55
18.0
13.5
3000 s
o
T = 65 C
18.5
19.0
10000 s
1000 s
19.5
20.0
20.5
21.0
Shear displacement [mm]
@20 degree-C, peak coefficient is independent of hold periods
@65 degree-C, peak value increases with increase of hold
21.5
Slide-Hold-Slide Friction Experiments
0.050
o
T = 20 C

0.040
o
T = 65 C

0.030
0.0082 per decade
0.020
0.026
0.010
0.0041 per decade
0.000
10
100
1000
10000
Hold time [s]
Frictional strengthening is likely due to augmentation in cohesion
(contact area) that may result from pressure solution
Scale Effects in Geo-hydrology – Space and Time
Lab scale
Field scale
Permeability, m2
10-10
?
10-14
10-18
10-1
100
101
102
Spatial Scale, m
103
Regional scale
Constitutive Relations for Transport Behavior
Approach
• The Challenge –
– Understanding rock-bursting and minimizing
impact
• The Opportunities –
– Understanding failure processes at field scale
and linking failure with source mechanisms
– Understanding fundamental rate and state
constitutive laws – and scale-up:
• In space
• In time
Five months of seismicity at Mponeng
Over 80,000 events
Colors grade from cool
to warm as events become
more recent
Creighton Mine, Canada
Approach
• The Challenge –
– Understanding rock-bursting and minimizing impact
• The Opportunities –
– Understanding failure processes at field scale and
linking failure with source mechanisms and event
scaling
– Understanding fundamental rate and state
constitutive laws – and scale-up:
• In space
• In time
Experimental Arrangement
Multiple pillars (of differing dimension)
constructed at multiple depths;
may include discontinuities
Experimental Arrangement
Monitoring Scales
•Run of facility
•Cavern
•Test
Fluid pressure
Flow and
reaction
Environmental Loads
•Excavation
•Excess fluid pressures
Monitoring and Testing
•Imaging – seismics & ERT – rupture types, sizes and locations
•Solid – stress, strain, extension, 4-D seismics, tilt
•Fluid – liquid and gas - pressure and composition – permeability and
reactive chemistry
How does this experiment
optimize the use of DUSEL?
Time, t
Principal Attributes
1.
Unusual spatial
scale – bridges
laboratory scale to
field scale
2.
Long-term access
3.
Depth gives stress
and thermal
regimes……
Spatial scale, x,y,z
Depth, z -> ; T
Important Questions
• Mechanisms of the triggering of rupture
• Mechanisms of strength-gain and fault-healing
– Role of reactive fluids
– Role of pressure solution and other mechanisms
• Understanding the transition - quiescent rupture and energetic
failure.
• Bridging the gap between laboratory and field scales
• Illuminating fundamental mechanics of Rate and State friction
constitutive laws
– Representation of seismic and interseismic fault behaviors
– Earthquake nucleation, coseismic rupture and earthquake afterslip
• Role of fault roughness and gouge on frictional properties and
stability
•
………………….
Expected Results
Address Issues Relating to:
• Stability of large openings against
energetic failure
• Improved understanding of the energetic
failure of rock
– Small scale for civil and mined underground
structures
– Large scale (space and time) for earthquake
mechanics
Experimental Requirements
• Contained and remote – possibly part of a “Large
Experiment” Facility
• Duration – Long term experiment (10y) on large volume
natural fault/fracture. Subsidiary short-term expts (~1,s to
~10,s of meters edge-dimension) for short term on block
periphery
• Reusability – Not likely for small experiments, possible
for large block.
• No compatibility with physics experimentation – except
monitoring of cavern excavation sequence
• Needs appropriate fault/stress/strength structure