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.


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.



Health and safety, productivity and environment initiatives.


Open Cut

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

Recently Completed Projects

C19024Establishing Ecologically Sustainable Mine Water Release Criteria In Seasonally Flowing Streams

Extreme rainfall conditions in the Fitzroy Catchment over an approxi...

C25030Coal Mine Open Pit Final Void Closure And Relinquishment - Addressing Uncertainty In Coal Mine Environmental Planning

This report addresses uncertainties faced by coal mine operators whe...

C27046Estimation Of True Deformation Vector From Slope Radar Monitoring

Slope deformation radar monitors are now widely used in open cut coa...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C27004Improving Coal Flotation With Oscillatory Air Supply

This report provides detailed information on coal flotation with os...

C25018Improving Solids Recovery And Moisture Reduction In Ultrafine Coal Dewatering

This report provides detailed information on fine coal dewatering in...

C27028Lab Froth Flotation Testing Guide With Coal Quality

Correct outcomes from laboratory froth flotation testing in coal bor...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

C26039Nanoporosity In Cokes: Their Origin, Control And Influence On CO2 Reactivity

This project using the outcomes of previous project C24060, examine...

C28063A Comprehensive Technical Review Of High-Efficiency Low-Emission (HELE) Pulverised Coal Combustion Technologies For Power Generation

Research and development has been undertaken worldwide to realise co...

C28064Carbon Structure Transformation During Coking Of Australian Coking Coals: Better Understanding The Coke Formation

Carbon structures of coke that are formed during the plastic layer a...

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) - Phase 2 Demonstration In A Packed Bed Reactor

An alternative approach to high temperature oxidation of ventilation...

C26004CFD Modelling Of Reverse Thermal Oxidisers For VAM Abatement - CFD Modelling Of Fixed-Bed RTO Devices

The project is part of a larger multi‐phase program of study a...

C27058Technological Assessment Of A Recycle Reactor For VAM Abatement

Underground coal mining emits high volumes of methane, diluted in ve...

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


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