Highwall mining

2. Highwall Mining

3. Presentation outline
 Highwall mining systems
 Geotechnical issues & rating
 Guidance Control
 Failures and causes
 Conclusions
Highwall Mining

4. Highwall Mining
 Driving parallel roadways into highwall/ coal seam using
remote controlled mining machinery – 200 - 500 m depth
Highwall Mining

5. Highwall Mining System (1)
 Addington Highwall Mining system
 Addcar system
Highwall Mining

6. Highwall Mining Systems (1) cont.
 Addcar System
 Launch vehicle
 Conveyor cars
Highwall Mining

7. Highwall Mining Systems (2)
 Archveyor system
Highwall Mining

8. Highwall Mining
Highwall Mining Systems (3)
 Auger system

9. Geotechnical Issues & Rating
 Unsupported span stability
 Pillar stability
 Panel Stability
 Case studies
 Design guidelines
Highwall Mining

10. 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

11. Highwall Mining
Pillar Stability
 Lab testing of coal strength
 Empirical approach
 Pillar stability modelling
 Applications and verification in field
P illa r S tre n g th v . W id th /H e ig h t
0
5
1 0
1 5
2 0
2 5
0 1 2 3 4 5
P il la r W id th /H e ig h t
PillarPeakStress(Strength)
P ro p o s e d H W M
W a g n e r
B ie n a w s k i
A ve ra g e Tre n d lin e
0.36W/h)(0.64*6.00 Strength
0.36w/h)(0.64*6.00 Strength
0.44w/h]w[0.69W 

12. 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

13. 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)
ConfidenceLevel(%)
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

14. 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

15. 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

16. Failures (1)
 Panel failure
Highwall Mining
Before After

17. Local panel failure at Yarrabee MinePanel failure at Ulan Mine
Highwall Mining
Failures (2)
 Panel failure

18.  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

19. 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

20. 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