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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