Robert Trueman - Golder Associates

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<ul><li><p>Improving Cavity Prediction on </p><p>Longwall Faces</p><p>ACARP C21013 Extension</p></li><li><p>Aims of Study</p><p> Develop reliable convergence and leg </p><p>pressure TARPs from shield monitoring </p><p>data that can give a pre-warning of </p><p>impending roof control problems</p><p> Determine the accuracy of the TARPs</p><p> An estimate of the duration of the pre-</p><p>warning</p><p> An indication of operational controls</p></li><li><p>Mines Where Analysis of Convergence, Tilt and </p><p>Pressure Monitoring has been carried out to date</p><p>Austar - CSIRO Tilt Sensors</p><p>Newlands - CSIRO Tilt Sensors</p><p>Narrabri Caterpillar Tilt Sensors</p><p>Broadmeadow Caterpillar Tilt </p><p>Sensors</p><p>Dendrobium Joy Tilt Sensors</p><p>West Wallsend Leg pressure only</p></li><li><p>Leg Pressure TARPs</p><p> A manual set pressure of 40 tonnes/m2</p><p>(about 180 Bar)</p><p>set pressures less than this are not </p><p>adequate to eliminate tension in the </p><p>subsiding roof plate</p><p>when are inadequate manual set </p><p>pressures a result of cavities and when </p><p>do they cause cavities? it is critical to </p><p>answer this question</p></li><li><p>Leg Pressure TARPs</p><p> A Pre- yield initial (within the first 5 </p><p>minutes) loading rate of 15 </p><p>bar/minute</p><p>this can be a very fragile signal, </p><p>particularly when high set pumps </p><p>are enabled</p><p>it infers rather than measures post-</p><p>yield convergence</p></li><li><p>Convergence TARPs</p><p> A cumulative convergence over 3 </p><p>consecutive load cycles of 200 mm</p><p>Convergence in a single load cycle of </p><p> 80 mm</p><p>An average convergence rate over the </p><p>entire cycle of 50 mm/hour</p></li><li><p>Convergence TARPs</p><p> The pre-yield loading rate TARP </p><p>would indicate a pre-yield </p><p>convergence rate trigger of about 1.5 </p><p>mm/min</p><p>not determinable with current OEM </p><p>sensors and difficult to determine </p><p>with CSIRO sensors without filtering</p></li><li><p>Significant Convergence Event</p><p> A post-yield convergence rate of 5 mm/minute has </p><p>been shown to be indicative of the onset of a major </p><p>convergence event</p><p> outside of the resolution of current OEM </p><p>sensors</p><p> not a TARP because occurs too late in the build </p><p>up to the event</p><p>measurements could nevertheless significantly </p><p>improve our understanding of the interaction </p><p>between the shield and the strata</p></li><li><p>October 25, 2016 9</p><p>How Much Notice of an Event?</p></li><li><p>October 25, 2016 10</p><p>How Much Notice of an Event?</p></li><li><p>Accuracy of the Trigger Levels</p><p> A detailed analysis indicated that the trigger levels </p><p>were successfully initiated before cavities occurred </p><p>about 80% of the time in the majority of the back-</p><p>analyses carried out.</p><p> The majority of the 20% where cavity detection in </p><p>advance was not successful were false positives </p><p> At Broadmeadow mine for LW9 the accuracy of the </p><p>trigger levels was about 80% for the first third of </p><p>the longwall and then apparently dropped to about </p><p>40% (this did not occur at any of the other mines)</p></li><li><p>TWAP for LW 9 Broadmeadow</p><p>October 25, 2016 12</p></li><li><p>Pre-Yield Loading Rate for LW 9</p><p>October 25, 2016 13</p></li><li><p>Convergence for LW 9</p><p>October 25, 2016 14</p></li><li><p>Average Closure Rate for LW 9</p><p>October 25, 2016 15</p></li><li><p>Cumulative Convergence for LW 9</p><p>October 25, 2016 16</p></li><li><p>Broadmeadow LW9</p><p> An analysis indicated that in the majority of </p><p>the cases where trigger levels were initiated </p><p>the tip height increased </p><p> It was hypothesised that cavities did occur </p><p>in the majority of the occasions where the </p><p>trigger levels were initiated but that </p><p>adequate set pressures were achieved by </p><p>the operators</p></li><li><p>Comparing with LVA TARPSBroadmeadow LW9 August 2014</p></li><li><p>October 25, 2016 19</p><p>Cumulative Success in Detecting Cavities for </p><p>LW 9</p></li><li><p>TWAP and Initial Loading Rate Maps for West </p><p>Wallsend Mine</p><p>October 25, 2016 20</p></li><li><p>West Wallsend Pre-yield Loading </p><p>Rate</p></li><li><p>Further Work</p><p> Confirm cavity detection using tip height is </p><p>valid</p><p> Improve cycle delineation within LVA </p><p>including sub shear TARP monitoring</p><p> Clearer delineation of the geological causes </p><p>of high level periodic weighting</p><p> Controls other than set pressure </p></li></ul>


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