evaluating the effectiveness of the 1750 tonne shields at moranbah north mine kelly martin mehmet...

Evaluating the Effectiveness of the 1750 Tonne Shields at

Moranbah North Mine

Kelly MartinMehmet KizilIsmet 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:DepthSandstone channelsFaultsPly 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

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

Aim:

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

• Converted LVA pressure and chainage data into real-time coordinates using Surfer

• Low pressure regions coloured red – indicate cavities (<250 bar)

LW107 LW108

Number of Low Pressure Regions

LW107 LW108

Total Number of Cavities with lost time 38 6

TG Cavities with lost time 4 4

Face Cavities with lost time 34 2

Geological Hazard Map

LW108

LW107

Cavities in Hazard Zones

Hazard Zone

Number of Low Pressure

Regions

LW107 LW108

Fault Zone Multiple 0

Ply Split Zone Multiple 10

GMR Split Zone 9 1

GMR Split and

Weighting Zone 6 3

Weighting Zone 41 1

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

• 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

LW108 TG Issues and Delays

Lost Time Due to Shield Issues

•48% less lost time in LW108 due to shield issues

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 from LVA Data

Shield Performance Around Cavity Zones

Posi-set pressure (bar) 400

Yield pressure (bar) 450

Posi-set pressure (bar) 410

Yield pressure (bar) 465

Shield Performance Around Cavity Zones

LW107 LW108

Percentage of time cavities were

encountered in panel (%)8.52 3.12

Percentage of time shields were at or

above yield pressure (%) 6.47 0.61

Shield Performance From LVA Data

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

Shield Rating in High Hazard Zones

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

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

Shield Suitability

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