1. Highwall Mining

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

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

4. Highwall Mining System (1) Addington Highwall Mining system l Addcar system Highwall Mining

5. Highwall Mining Systems (1) cont. l Addcar System t Launch vehicle t Conveyor cars Highwall Mining

6. Highwall Mining Systems (2) l Archveyor system Highwall Mining

7. Highwall Mining Systems (3) l Auger system

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

9. Unsupported Span Stability u Typical failure mechanism – delamination & snap-through u Simple analytical – thickness of roof plate, Y, u Probabilistic approach u Realistic prediction – Geology, rock properties

10. Highwall Mining Pillar Stability u Lab testing of coal strength u Empirical approach u Pillar stability modelling u Applications and verification in field

11. Highwall Mining Panel Stability u Panel stability depends on local mine stiffness u Panel factor of safety u One pillar failure may lead to total panel failure u Roadways to be driven in perfect parallel

12. 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. Highwall Mining Index (HMI) has been developed Highwall Mining

13. Guidance Control (1) l Driving parallel roadways  remote miner  200 to 500 m depth l Problems  Cut-through’s connection  Pillar failure - frequent roof falls  Limited penetration depth Highwall Mining

14. Guidance Control (2)  Problems to solve u Uncertainty in pillar size u Frequent cut-throughs u Reduced penetration depth u pillar/panel failure  Guidance system u Military grade Inertial Navigation System u Independent odometer u Controlling computers u Operator displace and interface  Achievements u Used in every HWM system in Australia u No mining equipment lost due to collapse u Penetration depths increased - 350m to 510m Highwall Mining

15. Failures (1) l Panel failure Highwall Mining BeforeAfter

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

17.  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

18. Production l Production ~ 1 million tonnes per year l Employees – 50 (High productivity – main advantage) l Continuous inert gas injection @ 150 l/s l Penetration depth – varies – 100 to 500 m (Av 300m)  Gas issues  Stability issues l Each roadway driven – almost in one day (or less) l Production share in Australia – 1% Highwall Mining

19. Conclusions l Main attraction – high productivity and low cost l Suitable for certain conditions – 500 m boundary l May lead to more fires and collapses l Around 50% of extraction l Creates problems for deeper reserves l Production share in Australia – 1% l Punch longwall – preferred for large reserves  High production and longer term view Highwall Mining