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Evaluating the Effectiveness
of the 1750 Tonne Shields at
Moranbah North Mine
Kelly Martin
Mehmet Kizil
Ismet Canbulat
Outline
• Project background
• Project aims and scope
• Methodology
• Results of analysis
• Summary of results
• Conclusions
Project Background
• Challenging geotechnical environment historically
resulted in cavity formation on the longwall face with
its associated reduction in productivity
• Complex geology:
Depth
Sandstone channels
Faults
Ply split and rider seam split
• Concerns raised about roof stability in future panels at
greater depths
• Determined that 1750t shields would be required to
adequately control strata
Project Background
Continued
• 1750t shields are highest capacity shields in the
world
• Replaced 980t shields due to:
 Aging duty
 Supports operating at yield for significant
periods
 Structural condition
 Increasing depths, complex geology and
associated geotechnical conditions
• 1750t shields installed at start of LW108 panel
Project Aim and Scope
Aim:
To determine the effectiveness of the new 1750 tonne shields
Scope:
• Data analysis was confined to parallel sections of LW107
and LW108
 Panels are adjacent to each other and are subject to
similar conditions
 Comparison of both panels using analysis results was
used to determine effectiveness of 1750t shields
• Only data related to cavity development and strata
control were analysed
Methodology
• LVA data sorted and converted into pressure contour maps
• Hazard map created using geological data and contour maps
• Identified and analysed:
 Number of cavities in each panel
 Cavity occurrences in hazard zones
 Lost time due to strata control issues
 Lost time due to shield issues
 Percentage of time spent at or above yield pressure
 Percentage of time cavities were encountered in panel
• Data analysis supplemented by:
 Deputy delay reports
 Fault maps
 Geological data
Leg Pressure Contours
LW107
LW108
• Converted LVA pressure
and chainage data into
real-time coordinates using
Surfer
• Low pressure regions
coloured red – indicate
cavities (<250 bar)
Number of Low
Pressure Regions
Total Number of Cavities with lost time
TG Cavities with lost time
Face Cavities with lost time
LW107
LW108
38
6
4
4
34
2
Geological Hazard Map
LW108
LW107
Cavities in Hazard Zones
Number of Low Pressure
Regions
Hazard Zone
LW107
LW108
Fault Zone
Multiple
0
Ply Split Zone
Multiple
10
9
1
Weighting Zone
6
3
Weighting Zone
41
1
GMR Split Zone
GMR Split and
Total Time Lost Due to
Strata Control Issues
•17% less lost time in LW108 due to strata control issues
Time Lost Due
to Face Cavities
•87% less lost time in LW108 due to face cavities
Time Lost Due
to TG Cavities
•82% more lost time in LW108 due to TG cavities
Lost Time Due to TG
Cavities Continued
LW108 TG Issues
and Delays
•
Double stress notch encountered at point corresponding to
LW107 install road
 Effects extended approx. 1 C/T (100m) into LW108 panel
 Intense additional TG support required causing delays
•
Large unmapped faults encountered perpendicular to face
 Led to major stoppages due to TG support issues
•
Additional delays due to gas levels unique to LW108
 Prevented immediate entry to TG to install secondary support
resulting in additional lost time
•
The final analysis of shield effectiveness should subsequently
only focus on strata control issues which occurred at the FACE
in order to provide an accurate comparative assessment
Lost Time Due
to Shield Issues
•48% less lost time in LW108 due to shield issues
Shield Performance
from LVA Data
LW107:
•
•
•
•
Constant fluctuations in shield pressures
Regularly operated at or above yield pressure
Regularly operated at significantly low pressures
Shields adjacent to cavity zones consistently in
yield
LW108:
• Relatively consistent shield pressures
• Rarely operated in yield
• Even around cavity zones resulting in increased
loading, the shields did not yield
Shield Performance
Around Cavity Zones
Posi-set pressure (bar)
400
Yield pressure (bar)
450
Shield Performance
Around Cavity Zones
Posi-set pressure (bar)
410
Yield pressure (bar)
465
Shield Performance
From LVA Data
LW107 LW108
Percentage of time cavities were
encountered in panel (%)
Percentage of time shields were at or
above yield pressure (%)
8.52
3.12
6.47
0.61
Overall Performance
Comparison
LW108
LW107
Number of Low Pressure regions
27
87
Time Lost (Face Cavities)(h)
20
148
Time Lost (Shields) (h)
314
603
Moderate - High
Low
Percentage of time cavities were
encountered in panel (%)
3.12
8.52
Percentage of time shields were
at or above yield pressure (%)
0.61
6.47
Shield Rating in High Hazard
Zones
Shield Suitability
Based on an acceptable yield percentage value of 5%:
 LW107
 shields not suited to the mining conditions
 Shields spent 6.47% of time operating at or above yield pressure
 Total time spent in yield would actually be significantly higher
 LW108
 More than adequate for mining conditions
 Shields spent 0.61% operating at or above yield pressure
 Total time spent in yield would be significantly higher
 In future panels at greater depths and increased loading it is
feasible to say that the 1750 tonne shields would be suitable to
the conditions
Conclusions
• LW108 performed significantly better in
geotechnical hazard zones
• Only 2 face cavities in LW108 with lost time
compared with 34 in LW107
• Almost half the time lost due to shield issues in
LW108
• 1750t shields found to be effective overall and
more than adequate for mining conditions with
greater potential for future panels
Anglo American Metallurgical Coal is acknowledged
with gratitude for the permission to publish this paper.
Steve Winter and Andrew Laws are thanked for their
willingness to share their knowledge and for providing
the necessary data for the project.
Thank you