ACARP ACARP ACARP ACARP
Open Cut

Geomechanical Factors Affecting Highwall Mining

Open Cut » Highwall Mining

Published: May 99Project Number: C5007

Get ReportAuthor: Mary Duncan Fama, M Craig, M Coulthard | CSIRO Exploration & Mining, M A Coulthard & Associates

CSIRO has developed highwall mining design techniques suitable for australian conditions.

Because highwall mining is reliant on the self-supported capacity of the rock mass, highwall stability, pillar design and stability of unsupported spans are major issues for highwall mining operators.

Project Objectives

The overall project objective is to provide the highwall mining industry with practical and reliable design techniques for span assessment and layout configuration for highwall mining under Australian conditions. Case studies were conducted at Oaky Creek, Moura, German Creek and Ulan highwall mining operations.

The project's specific objectives are to:

  • Accurately characterise the immediate roof of the Oaky Creek and Moura highwall mining sites and monitor their response to operations.
  • Use monitored data from Oaky Creek to test a range of predictive models for suitability and effectiveness.
  • Propose a preliminary predictive model after initial work at Oaky Creek. Following work at Moura, test and modify the model accordingly.
  • Fully report research findings and transfer these as effectively as possible to the mining industry.

As part of the project, researchers will:

  • Review highwall mining experience in Australia with a view to identifying the key factors which lead to stability or instability.
  • Verify the current span stability assessment models against mining experience under different roof conditions.
  • Improve layout design procedures by identifying the key factors affecting design and their relative importance via parametric study.

Findings

The research found that three major factors affected design of highwall mining pillars:

  • The average in situ mass coal strength.
  • The pillar width to height ratio.
  • The strength of the interfaces between the coal seam and the roof and floor when the whole thickness of the seam is mined.

The research also found the exact stiffness, strength or parting strength of relatively competent roof and floor material had little effect on the pillar strength.

A review of highwall mining experience at the four mines found that successful highwall mining operations required:

  • Site investigation to obtain comprehensive geological information.
  • Assessment of span stability in advance - if this is predicted to be poor, remedial measures, such as leaving coal in the roof of entries, need to be considered.
  • Layout designs that take account of pillar strength including interaction with roof and floor. Factors of safety on layout design must be adequate to ensure long-term stability.
  • Guidance of the continuous highwall mining system to preserve pillar and span integrity. The introduction of the Horta inertial navigation system has significantly improved highwall mining practice to the point where guidance has been virtually eliminated as a problem.
  • Critical panel width with barriers needs to be considered to isolate problems. Massive panel failure occurs when a sufficient number of entries are mined, usually when a critical panel width is reached. A highwall mining panel narrower than its critical width is unlikely to fail in a catastrophic manner, since stress concentration caused by local failure can still be sufficiently bridged away to the abutments. In contrast, a panel greater than its critical width will be much more vulnerable to a catastrophic "domino" failure due to insufficient stress bridging once a local failure is initiated. The critical panel width varies, depending on the roof geology and overburden depth.
  • Knowledge of in situ stress and stress concentration near the highwall, especially for benched highwalls.
  • Constant monitoring of mining conditions during operations.

Where To From Here

A second ACARP project (C8033 Optimal Design and Monitoring for Highwall Mining) is under way to develop integrated pillar/panel stability assessment guidelines.

The aims of the project are to:

  • Evaluate the likelihood of medium/long term stability and subsidence for highwall mining designs over a wide range of geological conditions, based on back-analysis of all pits in Australia that have been highwall mined.
  • Carry out a quantitative assessment of possible 3D stress concentration near the highwall face and its effect on mine stability, particularly under benched highwalls that may have suffered significant blast damage.
  • Integrate pillar and panel layout design guidelines that minimise the risk of catastrophic panel failure.
  • Test and evaluate a seismic monitoring system to provide early warning of the onset of large-scale instability.

This project is scheduled for completion by June 2001.

 

Underground

Health and safety, productivity and environment initiatives.

Recently Completed Projects

C26061The Young’S Moduli, Poisson’S Ratios And Poroelastic Coefficients Of Coals

This report describes the measurement of coal (and rock) properties ...

C24015 Assessment Of Convergence Based Roof Support Design For Longwall Abutment Loads

The aim of Stage two of project C24015 was to develop a roof support...

C25072New Approaches To Mine Gas Analysis And Ratios

The spontaneous combustion of coal remains a hazard in underground c...

Underground

Open Cut

Safety, productivity and the right to operate are priorities for open cut mine research.

Recently Completed Projects

C26022Real-Time Prediction Of Coal Top Through Guided Borehole Radar Wave Imaging For Open Cut Blast-Hole Drilling

Damage to the tops of coal seams caused by incorrect blast stand-off...

C26027Using An Ecotoxicological Approach To Validate The DGT Technique For The Measurement Of Bioavailable Metal Concentrations

This project builds on the opportunity identified through Project C2...

C25039Prediction Of Long-Term Salt Generation From Coal Spoils

The release of salts from spoil piles has the potential to affect su...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C250083D Flotation Of Fine Particles

In this project a process for the continuous, selective agglomeratio...

C20052Full Scale Gravity - Desliming Using Cascading REFLUX Classifiers

Considerable quantities of fine coal are disposed of as part of the ...

C26007 Revised Dustiness And DEM Test Method (Update Of AS4156.6) Part 2:Preparation

In 2015 project C23054 investigated and reviewed the Australian Stan...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

C25045Stage Two - Assessment Of In Situ High-Temperature Strength Of Cokes

Stage I of this project established a reliable and repeatable proces...

C27003Review Of ACARP Research To Support Marketing Of Australian Thermal Coal

In this project, researchers pinpointed issues relating to the use o...

C25044Trace Elements In Coal; Status Of Test Methods In Use And Their Applicability

 STAGE 1 REPORT

The key objectives of this stage...

Technical Market Support

Mine Site Greenhouse Gas Mitigation

Mitigating greenhouse gas emissions from the production of coal.

Recently Completed Projects

C27008Selective Absorption Of Methane By Ionic Liquids

The connection of a ventilation air methane (VAM) abatement plant di...

C24061Proof-Of-Concept Photocatalytic Destruction Of Methane For Coal Mining Fugitive Emissions Abatement

Australia's fugitive emissions in 2015 were 41 Mt CO2-e (representin...

C23052Novel Stone Dust Looping Process For Ventilation Air Methane Abatement - Phase 3

This multi‐phase project is concerned with the mitigation of m...

Mine Site Greenhouse Gas Mitigation

Low Emission Coal Use

Step-change technologies aimed at reducing greenhouse gas emissions.

Recently Completed Projects

C17060BGasification Of Australian Coals

Four Australian coals were trialled in the Siemens 5 MWth pilot scale ga...

C17060AOxyfuel Technology For Carbon Capture And Storage Critical Clean Coal Technology - Interim Support

The status of oxy-fuel technology for first-generation plant is indicate...

C18007Review Of Underground Coal Gasification

This report consists of a broad review of underground coal gasification,...

Low Emission Coal Use

Mining And The Community

The relationship between mines and the local community.

Recently Completed Projects

C16027Assessing Housing And Labour Market Impacts Of Mining Developments In Bowen Basin Communities

The focus of this ACARP-funded project has been to identify a number...

C22029Understanding And Managing Cumulative Impacts Of Coal Mining And Other Land Uses In Regions With Diversified Economies

The coal industry operates in the context of competing land-uses that sh...

C23016Approval And Planning Assessment Of Black Coal Mines In NSW And Qld: A Review Of Economic Assessment Techniques

This reports on issues surrounding economic assessment and analysis ...

Mining And The Community

NERDDC

National Energy Research,Development & Demonstration Council (NERDDC) reports - pre 1992.

Recently Completed Projects

1609-C1609Self Heating of Spoil Piles from Open Cut Coal Mines

Self Heating of Spoil Piles from Open Cut Coal Mines

1301-C1301Stress Control Methods for Optimised Development...

Stress Control Methods for Optimised Development and Extraction Operations

0033-C1356Commissioned Report: Australian Thermal Coals...

Commissioned Report: Australian Thermal Coals - An Industry Handbook

NERDDC