1. North Goonyella Mine Longwall Health, 8th June 2017
Gavin Lowing
Principal Geotechnical Engineer

2. NGC
North Goonyella Coal (NGC) is an underground longwall coal mine located 160 kilometres west of Mackay in the Bowen Basin, producing a premium quality coking coal.
NGC coal is exported through the Dalrymple Bay Coal Terminal, south of Mackay to global seabourne demand centres .
In 2015, North Goonyella produced 2.7 million tons (2.4 million tonnes) of saleable coal

3. North Goonyella Mine

4. NGC
Longwall Health
Transitioned from conventional longwall to longwall top coal caving (LTCC) in 2014 (LW7N to LW8N)
LTCC is under a partnership deal where Yanzhou owns the longwall and will share in the additional coal produced by using the technology.

5. NGC
Geotechnical Considerations
Lower face extraction height – provides a more stable longwall face with less strata failure delays (Moodie, 2011)
Operating cost reductions – potential double (or more) returns of longwall recoverable tonnes, per metre of gateroad development (Hebblewhite and Cai, 2004)
That is only if the system has been designed to consider local geotechnical conditions
Sadly in the race to embrace new technologies and the potential to double returns our old friend ‘strata conditions’ gets left behind
Strata conditions can make or break a longwall; whether conventional or LTCC

6. NGC
Geotechnical Considerations
The design of the LTCC system at NGC did not take into account potential strata issues such as cavities forming in the MG (stress notch conditions), weighting from the goaf (blocky roof material) and a caving sequence that enable maximum recovery (no numerical modelling)
As a result we’ve had numerous cavities in front of MG shields 1 to 3 impact production
Severe weighting on the rear shields that disabled the rear AFC drive – the drive design was too large
This is because cavities/blocky material allowed the three legged shields to rotate upwards at the face and sit down on the rear AFC drive – rear AFC drive design was too large for conditions
In late 2016 the decision was taken to ‘set free’ the rear AFC drive into the goaf
Cavities in front of the MG shields are still an issue

7. NGC LW9N Example
Hazard Plan

8. NGC LW9N Example
LVA Data

9. NGC LW9N Example

10. NGC LW9N Example

11. NGC LW9N Example

12. NGC LW9N
Decided to use Fenoflex to consolidate the fractured ground ahead of the face
Top hole 9m long and bottom hole 11m
‘W’ type pattern
Currently still ironbound and unable to move.
Need to get chocks down, double chock, clean up and retreat face

13. NGC LW9N Example
Maingate Issues

14. Installation of additional 11m Megabolts/14m Trussed Cables
NGC LW9N Example
Maingate Issues
Rocsil fill material
The continued installation of wooden props along the pillar side ribline until such time as conditions improve
The installation of additional support (Megabolts and spot-bolts) as required. 
Install additional 4-way Tell Tales to determine roof behavior, Tell Tales to be installed biased towards the centre of the roadway.
Installation of additional 11m Megabolts/14m Trussed Cables

15. Its too late by the time the gear arrives on site!
NGC
Take Away Points
Geotechnical due diligence is an essential consideration in any longwall system
Make yourself known to the stakeholders and give them your assessment – (put it on the record)
Its too late by the time the gear arrives on site!