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

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Highwall Mining Systems (2)

Archveyor system

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Highwall Mining

Highwall Mining Systems (3)

Auger system

Geotechnical Issues & Rating

Unsupported span stability Pillar stability Panel Stability Case studies Design guidelines

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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

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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

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Failures (1)

Panel failure

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Before After

Local panel failure at Yarrabee MinePanel failure at Ulan Mine

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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

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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