Optimal Design and Monitoring for Highwall Mining

This is the final report for the ACARP research project, C8033, "Optimal Design and Monitoring of Layout Stability for Highwall Mining". The aim of the report is to provide general guidelines for highwall mining design. The guidelines will help guide mining engineers through the process of feasibility evaluation to final execution of highwall mining in their mining lease. Purely economic matters, however, are not addressed. A number of new tools for feasibility studies, including the Highwall Mining Index (HMI), the Auger Mining Index and Percentage Extraction estimate are presented in the report.

The key components of this report include:

• Feasibility study. The geotechnical evaluation to determine whether the site is suitable for highwall mining. A highwall mining index method is presented to help the decision making process in Chapter 2.
  
  
• Site investigation. If the site is considered likely to be a suitable site for highwall mining, geological and geotechnical investigation in the mining reserve (e.g., drilling, highwall mapping, highwall hazard identification etc.) includes the gathering of data for layout design. The new data can also refine the results of the feasibility study. Guidelines for conducting the site investigation are outlined in Chapter 3.
  
  
• Span stability assessment. Evaluation of the stability of the entry spans, which are unsupported, to ensure the success of mining. This needs to be investigated before the commencement of mining. Assessment tools and methodology are presented in Chapter 4.
  
  
• Layout design. A layout design to specify pillar size and whether barrier pillars are to be left between panels. An optimal layout design will maximise the recovery whilst minimising the risk of unacceptable instability. Pillar design tools and a new panel stability theory are presented to help in the evaluation in Chapter 5.
  
  
• Design verification against past experience. A number of panel/roof instabilities have been recorded in the past. A selection of these have been back-analysed and the major causes of the instabilities summarised in Chapter 6. Lessons learned from these studies may be used to provide a final check of the design for the current site.
  
  
• Mining operation and feed-back. Monitoring of the stability of the highwall, spans and pillars during mining are critically important to a continuous, smooth mining operation. After mining operations have commenced with the designed layout, mining difficulties may occur if unexpected ground conditions are encountered. This may necessitate a change in layout design. Guidelines for conducting monitoring and information feed-back during mining are provided in Chapter 7.
  
  The final report is presented in a user-friendly web style format. Most of the new tools developed within this project, including the Highwall Mining Index (HMI) and Percentage Extraction estimate, are provided in interactive forms. These interactive tools make it easy for users to perform their own evaluation of a site for highwall mining.