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Rib Support Design Methodology for Australian Collieries

Underground » Strata Control and Windblasts

Published: November 04Project Number: C11027

Get ReportAuthor: Mark Colwell | Colwell Geotechnical Services

The aim of this project was to provide the Australian coal industry with a rib support design methodology and computer based design tool that can be utilised by colliery engineers and geologists who have sufficient experience and training in relation to underground coal mine strata mechanics. These aims have been achieved and the design methodology and software package is referred to as Analysis and Design of Rib Support (ADRS). The intended benefits to underground operations, in the provision of this information and resource, are a safer and more productive workplace.

The safety of personnel is the "key driver" for this research and a safer workplace should result in a more productive workplace. In addition to safety, rib instability can negatively impact on productivity or development rates

Based on information supplied by the Department of Natural Resources and Mines, QLD and Coal Services Pty Ltd it was found that for the years 1997 to 2003 there were 175 Lost Time Injuries (LTIs) as a result of roadway rib spall. During that period this included one fatality in NSW, which it is understood occurred during the installation of support off the continuous miner and two fatalities in QLD. In relation to the QLD fatalities it is understood that on both occasions the person was working by the side of the continuous miner but back from the development face and not in the process of installing roof or rib support.

Approximately 40% of rib related LTIs occur during the installation of ground (roof or rib) support off the continuous miner (referred to as Category 1 incidents), while around 65% occur on or about the miner and therefore clearly it is this "zone" where it is most likely that injuries due to rib spall will occur. ADRS cannot directly assist in preventing the 40% of incidents that occur either just prior to or during the ground support installation process. However given the significant occurrence of injuries at this locality and stage of the mining cycle the project has attempted to address this issue in a more subjective manner.

A trouble shooting section has been included drawing on both the site inspections and additional information provided by several collieries and manufacturers in an attempt to share industry knowledge and solutions. ADRS can directly assist in the prevention of rib related incidents occurring outbye of the development face or about the longwall. In these situations personnel would be exposed to ribline which has been assessed and supported accordingly in terms of the design methodology.

ADRS provides a Design Rib Support Rating (Design RIBSUP) and guidelines in relation to the use of liners and cuttable/steel support to provide the end user with a workable technique. The rib support hardware component of the software assists the strata control engineer with the selection of suitable products and rib support patterns to satisfy the Design RIBSUP. Also within the software package a database search can be conducted to assist in the design process.

The design methodology deals with two types of roadway development:

  • Mains development and,
  • Gateroad development specific to Australian longwall mines.

The most significant difference affecting the application of rib support is that gateroad riblines will be subject to future longwall abutment loading, while mains development is not.

After numerous analyses using various outcomes, it was decided that a risk based assessment/outcome which took into account both the volume of spall and certain satisfactory/unsatisfactory criteria was the most appropriate to assist in formulating the design methodology. Furthermore, utilising a risk based outcome allows for a greater level of engineering and operational judgement and as a result ADRS can more readily (and is designed to) be incorporated as part of the minesite risk assessment process during the development of a colliery's Support Rules and Strata Management Plan (SMP).

Assessing risk is not an exact science and while guidelines and some set criteria are necessary, utilising engineering judgement is just as important. Therefore ADRS is not a prescriptive technique, but a tool to assist collieries in assessing their rib support requirements in the context of a properly facilitated minesite risk assessment.

To use ADRS it is critical that the recommended levels of rib support and how that support would be implemented is assessed within the framework of a properly facilitated risk assessment being a team exercise that draws on the experience of the colliery staff and employees. Where possible this should include (but is not limited to) the mine manager, longwall & development coordinators, strata control engineer, mine geologist and representatives of the longwall & development crews.

In terms of gateroad development the methodology differentiates between the rib support requirements associated with the belt road and that of the travel road, with the travel road also becoming the tailgate of the subsequent longwall panel. However the design methodology does not differentiate between the blockside and chain pillar side riblines in relation to the recommended level of support (ie Design RIBSUP) or the guidance provided concerning the type of support hardware that should be employed to satisfy the proposed level of risk.

In general, collieries would clearly prefer to use either no rib support or cuttable support without mesh in relation to the blockside ribline so as to reduce the risk of certain issues associated with the longwall face extraction/cutting process. For example:

  • Belt damage.
  • Blockages due to mesh.
  • Sparks associated with cutting steel bolts.
  • Mesh getting caught around the shearer.

It is the colliery's decision on how to "balance" the safety/productivity risks associated with the longwall extraction process and those safety/productivity risks associated with gateroad performance. The rib support design methodology should provide sufficient information so that a colliery can more rationally assess the risk in relation to rib performance and therefore make a more informed decision.

The competing interests of production and safety as well as development rates and longwall extraction issues will inevitably arise during the risk assessment as they should. Without question safety must take precedence over all other issues. Once again it is the colliery's decision and responsibility on how to balance the competing interests while providing a safe working environment. The ADRS Design Methodology is one (albeit significant) level of input to assist with this process.

To be consistent with current Australian underground coal mining practice the following two interconnected statements are the Fundamental Design Criteria to successfully using the ADRS Design Methodology:

  • The overall design should not compromise safety.
  • Therefore any design proposed by adrs (which may also incorporate a stepwise process in moving from current to optimum levels) should be part of a strata management plan that has assessed the risk and incorporates an appropriate level of continued monitoring and assessment.

The above two statements should be to the forefront of the reader's and user's mind when reviewing the report and/or using the ADRS Design Methodology and software.

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