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Highwall Mining
Presentation outline Highwall mining systems
Geotechnical issues & rating
Guidance Control
Failures and causes
Conclusions
Highwall Mining
Highwall Mining Driving parallel roadways into highwall/ coal seam using
remote controlled mining machinery – 200 - 500 m depth
Highwall Mining
Highwall Mining System (1)
Addington Highwall Mining system Addcar system
Highwall Mining
Highwall Mining Systems (1) cont.
Addcar System Launch vehicle Conveyor cars
Highwall Mining
Highwall Mining Systems (2)
Archveyor system
Highwall Mining
Highwall Mining
Highwall Mining Systems (3)
Auger system
Geotechnical Issues & Rating
Unsupported span stability Pillar stability Panel Stability Case studies Design guidelines
Highwall Mining
Highwall Mining
Unsupported Span Stability Typical failure mechanism – delamination & snap-through
Simple analytical – thickness of roof plate, Y,
Probabilistic approach Realistic prediction – Geology, rock properties
Highwall Mining
Pillar Stability
Lab testing of coal strength Empirical approach Pillar stability modelling Applications and verification in field
P i l l a r S t r e n g t h v . W i d t h / H e i g h t
0
5
1 0
1 5
2 0
2 5
0 1 2 3 4 5
P i l l a r W i d t h / H e i g h t
Pil
lar
Pe
ak
Str
es
s (
Str
en
gth
)
P r o p o s e d H W M
W a g n e r
B i e n a w s k i
A v e r a g e T r e n d l i n e
0.36W/h) (0.64*6.00 Strength
0.36w/h) (0.64*6.00 Strength
0.44w/h]w[0.69W
Highwall Mining
Panel Stability
Panel stability depends on local mine stiffness Panel factor of safety One pillar failure may lead to total panel failure Roadways to be driven in perfect parallel
Design Guidelines
15 key factors are considered, e.g. roof condition; mine reserve etc.;
Key factors are weighted differently in HMI;
Uncertainty on judgement is incorporated.
A given site has two index values: HMI rating, confidence level.
Recommendation is given for any HMI/Confidence ratings.
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
Highwall Mining Index (HMI)
Co
nfi
den
ce L
evel
(%
)
1
Good site for CHM mining
2
Possibly a good site for CHM mining. More information is need.
3
Site apparently unsuitable for CHM mining. Further
evaluation may be needed if new information is available
4
Site unsuitable for CHM mining.
Transition zone
Example pit 1
• Highwall Mining Index (HMI) has been developed
Highwall Mining
Guidance Control (1)
Driving parallel roadways remote miner 200 to 500 m depth
Problems Cut-through’s connection Pillar failure - frequent roof falls Limited penetration depth
7424250
7424300
7424350
7424400
7424450
7424500
7424550
7424600
7424650
7424700
7424750
707000 707100 707200 707300 707400 707500
panel 4#41-67
panel 3#21-40
panel 2#11-20
panel 1#1-10
Cracks on top of the highwall-Survey data
Cracks on the face of the highwall - Observation
North
Highwall Mining
Guidance Control (2)
Problems to solve Uncertainty in pillar size Frequent cut-throughs Reduced penetration depth pillar/panel failure
Guidance system Military grade Inertial Navigation System Independent odometer Controlling computers Operator displace and interface
Achievements Used in every HWM system in Australia
No mining equipment lost due to collapse
Penetration depths increased - 350m to 510m
Highwall Mining
Failures (1)
Panel failure
Highwall Mining
Before After
Local panel failure at Yarrabee MinePanel failure at Ulan Mine
Highwall Mining
Failures (2)
Panel failure
Lack of site investigation Poor knowledge on span stability Inadequate pillar design Poor guidance control Critical panel width Lack of knowledge on insitu stresses No monitoring and feedback
Factors contributing to pillar/panel failures
Highwall Mining
Production Production ~ 1 million tonnes per year Employees – 50 (High productivity – main advantage)
Continuous inert gas injection @ 150 l/s Penetration depth – varies – 100 to 500 m (Av 300m)
Gas issues Stability issues
Each roadway driven – almost in one day (or less) Production share in Australia – 1%
Highwall Mining
Conclusions Main attraction – high productivity and low cost Suitable for certain conditions – 500 m boundary May lead to more fires and collapses Around 50% of extraction Creates problems for deeper reserves Production share in Australia – 1%
Punch longwall – preferred for large reserves High production and longer term view
Highwall Mining