ACARP ACARP ACARP ACARP
Open Cut

Geotech Monitoring for Safety in Highwall Mining, German Creek Mine - Number C3053.1

Open Cut » Highwall Mining

Published: July 96Project Number: C3053

Get ReportAuthor: Ian Follington, Brett E Leisemann, Mary Duncan Fama, Baotang Shen | CSIRO Exploration & Mining

The success of highwall mining operations depends on

  • accurate prediction of roof strata behaviour in unsupported workings,
  • safe evaluation of highwall stability and pre-treatment, and
  • on a reliable method of pillar design to safeguard against collapse of the working area.

Additional factors influencing the viability of highwall mining are the impact of geological structure on unsupported roof and the consequences of undermining water filled abandoned highwall entries by conventional longwall extraction.

As highwall mining is newly introduced to Australia there is no background experience of highwall mining in Australian conditions upon which to base design parameters or make engineering judgements. In order to ensure safe and successful commercial application it will be necessary to invest in careful site investigation and evaluation of geological conditions together with the application of appropriate geotechnical monitoring for safety and design performance. Much of this will be research oriented until proven design methods based on practical experience can be derived.

In December 1993 Capricorn Coal Management Pty. Ltd. were awarded ACARP funding for a two year research project, C3053, to address the aims outlined below;

To develop a mathematical basis for the design of pillar widths using a combined narrow and wider partition pillar geometry, and for heading widths based on the tensile strengths of the immediate roof beams.

To geotechnically monitor the highwall, pillars and mined headings to ensure that maximum extraction is being achieved while maintaining adequate factors of safety, and to obtain data for back analyses of design criteria.

To monitor rate of in flow of seepage water into mined, sealed headings using piezometers and to address practical dewatering systems to avoid in flow into subsequent underground workings and

To transfer highwall mining technology throughout Australia.

This report specifically documents activities associated with aims 2 and 4 above and summarises work undertaken with regard to aim 1. The activities associated with aim 1 are documented in full in Ward et al 1993 and Moelle and Li 1993.

Unfortunately the full program of activities planned as part of aim 2 could not be completed. Those activities which were able to be completed are described below together with detailed records of operational experience.

Project Background

The German Creek Mining Lease is operated by Capricorn Coal Management Pty. Ltd. (CAPCOAL) and is located 80 kilometres north-east of Emerald in Central Queensland. Open cut mining commenced in 1981 in the German Creek Formation, extracting coal from 3 individual seams, resulting in the development of 10 open cut pits up to the present day. The majority of these pits have reached their economic limit in terms of stripping ratio, resulting in final highwalls.

These highwalls were generated as part of normal strip mining operations and as a result were not specifically designed or engineered with highwall mining in mind. The German Creek Highwall Mining Project was carried out by CAPCOAL and commenced in 1993 to examine the geological and geotechnical feasibility of highwall mining to extract coal from final highwalls (Ward et al, 1993).

Mechanised highwall mining commenced on site in November 1994, using an Addcar Highwall Mining System operated by Eltin Highwall Mining Pty. Ltd. perations began in Pit R in the Aquila Seam. Operations were moved to Pit A in the German Creek Seam in April 1995.

Conclusions

Highwall mining at German Creek Mine was disappointing for all parties concerned. Many of the reasons for this are beyond the brief of this study, but from a geotechnical point of view many of the problems associated with span instability could have been better predicted.

An early recognition of the in situ condition of the immediate roof in both Pit R and Pit A could have changed the way the whole site was approached. If this had been done it may well have led to the selection of alternative highwall mining technology better suited to the site conditions and operational environment.

The geotechnical design for the coal pillars performed well in Pit R and only experienced problems in Pit A when operational procedures were varied from those planned.

The assumptions made in the early planning of the layout design appeared to be well founded from the results of the back analysis of the pillar instability in Pit A. The cyclic nature of final entry depths would suggest that the incorporation of barrier pillars may well have had a disruptive influence upon entry stability.

However the understanding of the rock mass response to highwall mining is not yet well enough developed to be conclusive as to the relative merits of barrier pillars in all situations. The data from German Creek, the second highwall mining site in Australia, provides significant information to assist in the future development of highwall mining operations in Australia.

A number of conclusions can be drawn from the work presented in this report based on the data gathered from highwall mining operations at German Creek;

  • the structural condition of the immediate roof was not fully assessed in advance of operations at German Creek
  • the span stability assessment technique employed proved to be insensitive to the ground conditions and designed spans performed poorly
  • the inclusion of barrier pillars appeared to detrimentally influence the final depth of entries
  • analysis of layout design indicated that barrier pillars may act to reduce overall layout stability and limit recovery
  • the mining records would appear to show a pattern to entry depth on two levels, intra-panel and inter-panel
  • suitable pre-feasibility and feasibility studies should be conducted at potential future sites in advance of any commitment to a mining technology, to ensure best match between system and ground conditions
  • the coal seam should be mapped at future sites to check for the presence of in-seam shearing,and minor scale jointing/folding etc.

Operators should have sufficient information available to be able to select a level of design risk associated with highwall, pillar and span design with which they are comfortable and which matches the reward (i.e. recovery).

This approach can only be based on the identification of the dominant geotechnical factors at any site coupled with an understanding of how they impact upon system selection and operational procedures.

This project has added valuable information to the Australian database of highwall mining knowledge and assisted in improving the level of understanding of the impact of geological features upon operational performance.

 

Underground

Health and safety, productivity and environment initiatives.

Recently Completed Projects

C34019Longwall Bretby Cable Handling Monitoring With Fibre Optics

This project examined the potential of using fibre optic sensing tec...

C27049Mine Machine Radar Sensor Integration

The aim of this project was to develop an integrated radar sensor an...

C29007Innovative Coal Burst System To Investigate The Influence Of Confinement Loss And Pre-Conditioning On Coal Burst Mechanism

The challenges associated with designing and operating a safe and pr...

Underground

Open Cut

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

Recently Completed Projects

C33035High Water Recovery, Low Cost Desalination Using PV-Powered Membrane Capacitive Deionisation (Mcdi)

Capacitive deionization is a robust, energy efficient and cost effec...

C28035Topsoil Deficits In Site Rehabilitation Accelerated Transformation Of Spoils To Functional Soils

The incorporation of commercial biological amendments (compost, worm...

C34036Tyre Handler Testing Rig Stage 2: Lifting Trials

Tyre handling is a major source of risk in surface mining operations...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

C34060In-Situ Investigation Of Coke Structure Formation Under Stamp Charged Coking Conditions

Stamp charged cokemaking has emerged as an effective technique to im...

C34062Improving The Classification Of Microstructure Distribution In Coke CT Images Using Deep Learning And Lineal Path Calculations

This project builds on a number of earlier projects that have helped...

C29071Source Of Variability Of Reactivity Of Coke In The CSR Test

The Coke Strength after Reaction (CSR) test is used worldwide to det...

Technical Market Support

Mine Site Greenhouse Gas Mitigation

Mitigating greenhouse gas emissions from the production of coal.

Recently Completed Projects

C28076Selective Absorption Of Methane By Ionic Liquids (SAMIL)

This third and final stage of this project was the culmination of a ...

C29069Low-Cost Catalyst Materials For Effective VAM Catalytic Oxidation

Application of ventilation air methane (VAM) thermal oxidiser requir...

C23052Novel Stone Dust Looping Process For Ventilation Air Methane Abatement

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