Harris

Report
HIGHWALL STABILITY DUE
TO GROUND VIBRATIONS
FROM BLASTING
Dr. Kyle A. Perry
Dr. Kot F. Unrug
Kevin Harris
Michael Raffaldi
PURPOSE
Objective: Study the effect of blast vibrations
on the stability of highwalls and web and
barrier pillars
Methods
• Numerical Modeling
• Field Testing
• Laser Scanning
• Vibrations Monitoring
PROGRESS
SASW Testing
Numerical Modeling
• FLAC3D – Web and Barrier Pillars
– Stress Distribution
– Pillar Stability
• 3DEC – Highwall Modeling
– Laser Scanning
– Displacement/Velocity
Field Data Collection
SASW Testing
Dynamic Material Properties
• Shear Modulus
• Damping Ratio
Modulus/Damping Reduction Curves
• Dynamic Model Calibration
• Iterative Numerical Process
SASW Testing
4000
Surface Wave Velocity (ft/s)
Experimental
Theoretical
3000
2000
1000
0
3
4
5
6
7 8 9
2
3
4
10
5
6
7 8 9
100
Wavelength (ft)
2
3
Numerical Modeling
Sub-Objective 1: Evaluate the influence of
highwall mining progression on web/barrier
pillar stability using FLAC3D
Methodology
• Simplification – 2D Section
• Validation – Mark-Bieniawski
• 5 Case Studies
Material Properties
Coal Material Model
• Strain Softening Mohr-Coulomb
Roof/Floor Interface
• Bi-linear Mohr-Coulomb
2.5
Value
Elastic Modulus (GPa)
3
Poisson Ratio
0.25
Cohesion (MPa)
Initial
1.81
Final
0.41
Friction Angle (deg)
28
Plastic Strain Range
0.015
Shear Stress (MPa)
Property
2
1.5
1
0.5
0
0
1.15
2.3
3.45
4.6
Normal Stress (MPa)
5.75
6.9
Material Properties
Rock Material Model
• Ubiquitous Joint Model with Softening
UCS
SS
SH
MPa
100
30
Elastic
Modulus
GPa
40
10
Rock Matrix Properties
Poisson Friction
Cohesion
Ratio
Angle
--Deg
MPa
0.25
40
13.52
0.25
20
7.3
SS
SH
Cohesion
Maximum Residual
MPa
MPa
13.52
0
7.3
0
SS
SH
Cohesion
Maximum Residual
MPa
MPa
6.76
0.68
0.5
0.05
Range*
--0.005
0.005
Range*
--0.005
1.005
Tensile
Strength
MPa
5.8
1.74
Dilation
Deg
12
19
Matrix Softening
Tensile Strength
Maximum Residual Range
MPa
MPa
--5.8
0
0.001
1.74
0
0.001
Bedding Plane Softening
Tensile Strength
Maximum Residual Range
MPa
MPa
--4.64
0
0.001
0.17
0
0.001
Bedding Plane Properties
Friction
Tensile
Cohesion
Angle
Strength
deg
MPa
MPa
30
6.76
4.64
7
0.5
0.17
Dilation
Maximum Residual
Deg
Deg
12
0
19
0
Range*
--0.005
0.005
Dilation
Maximum Residual
Deg
Deg
12
0
19
0
Range*
--0.005
0.005
Model Validation
100
25
90
20
15
80
10
70
5
0
0
2
4
6
W/H Ratio
Mark-Bieniawski
8
Model
10
12
Stress (MPa)
Peak Strength (MPa)
30
60
50
40
30
20
10
0
0
2
Pillar 1
4
6
Distance Into Rib (m)
Pillar 2
Pillar 3
Pillar 4
8
Model Validation
18
16
15
14
28
13
26
12
11
10
0
0.2
0.4
0.6
W/L Ratio
0.8
1
Peak Strength (MPa)
Peak Strength (MPa)
17
24
22
20
18
16
14
12
10
2.5
3.5
4.5
5.5
6.5
W/H Ratio
Mark-Bieniawski
Model (Elastic)
Model (SS)
Model(SH)
7.5
Model Validation
Material Properties
• Peak Strength
• Calibration Reasonable
Web/Barrier Pillars
• “Infinite Length” Assumption
2D Cross Section
• Plane Strain Validation
Case Study Results
Case
Height (m)
Web (W/H)
Barrier (W/H)
Cover (m)
C1
1.219
0.75
3
45.7
C2
1.219
1
4
60.9
C3
1.219
1.25
4
70.1
C4
1.219
1.5
5
91.4
C5
1.219
1.75
6.5
118.9
8.00
7.00
6.00
5.00
SSTONE
4.00
ELASTIC
SHALE
3.00
TRIB. AREA
2.00
1.00
0.00
Average Barrier Stress (MPa)
Average Web Stress (MPa)
8.00
7.00
6.00
5.00
SSTONE
4.00
ELASTIC
SHALE
3.00
TRIB. AREA
2.00
1.00
0.00
CS1
CS2
CS3
CS4
CS5
CS1
CS2
CS3
CS4
CS5
Mining Progression Results
100%
98%
96%
94%
92%
CS1
CS2
90%
CS3
CS4
88%
CS5
86%
84%
82%
80%
Web 1Web 2Web 3Web 4Web 5Web 6Web 7Web 8Web 9 Web
10
Important Findings
Tributary Area Loading
• Common Assumption
• Arching Effect – Geology Dependent
• Importance of Barrier Pillar Design
Mining Progression
• De-stressing near Barriers
• Asymmetric Loading
Probability of Pillar Failure/Highwall Collapse
Dynamic Impact on Web/Barrier Pillars
Numerical Modeling
Sub-Objective 2: Correlate active highwall
sites with 3DEC for validation and additional
testing
Methodology
• Routine trips collect scan data
• Digitize geometry for mesh generation
within 3DEC
Primary Mine Site
Pine Branch Mine
• Perry County, KY
• Mountaintop/Contour
• Hazard 7 – Hazard 10 seams
• 200’ – 300’ Highwall
• Massive Sandstone
Important Mine Data
• Corehole Data
• Mapping
Primary Mine Site
VIBRATION AND SCAN DATA
Laser Scanning
• Pre/Post Blast Capture
• Mesh Generation for 3DEC
• Geologic Data
– 2 Primary Joint Sets
– 85 Degree Dip
– 110, 185 Direction
Seismograph Deployment
• Highwall Peak and Bottom
• Single Event Vibration Data
SUMMARY
HIGHWALL
STABILITY STUDY
FIELD DATA
MODELING
DESIGN
LIDAR
CALIBRATION
FIELD
TESTING
COMPLETED
MODEL
VIBRATION
RECORDS
BLAST AND DAMAGE
CORRELATION
LITERATURE/
EMPIRICAL
NUMERICAL
STUDY
DRAW
CONCLUSIONS
Project Direction
FLAC3D Modeling
• Probability of Pillar Failure/Highwall Collapse
• Dynamic Impact on Web/Barrier Pillars
3DEC Modeling
• Solidify Static Model
• Quantify/Correlate Damage and Vibrations
• Sensitivity Studies
– Ratio of PPV
– Geology
– Highwall Geometry
QUESTIONS?

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