ACARP ACARP ACARP ACARP
Underground

Determination of Goaf Delamination Horizons and Other Roof Geomechanical Features using Downhole Acoustic Logs

Underground » Geology

Published: January 02Project Number: C9003

Get ReportAuthor: David Green, Barry Ward | Green Exploration & Mining Services, Geotechnical Consulting Services

This project has sought to utilise the acoustic scanner log and the sonic log to detect and define features within the overburden of a coal seam which control roof stability and goaf formation. In order to do this it was first necessary to validate the features interpreted from the scanner by comparison to core and other commonly used methods. To determine the usefulness of the sonic log it was compared with historical extensometer data. This work has resulted in the following conclusions:

  • interpretation of the acoustic scanner image recognises more than 50% of fractures logged from core, with the advantage of determining the dip and direction of every feature interpreted
  • the acoustic scanner can identify additional fractures and lithological features from sections of the borehole with broken or missing core
  • planes of weakness are identified by the acoustic scanner which are not recorded by initial core logging, but which are confirmed by later inspection
  • recording of bedding breaks from core does not relate well to the definition of weak bedding planes in the acoustic scanner image
  • interpreted features matched with fractures identified by core logging provide clearly defined sets which agree with in-situ observations
  • breakout identified by the acoustic scanner provides a reliable and cheap indicator of the principal stress direction, and an indication of its magnitude
  • the acoustic scanner can be used in isolation or in combination with other geophysical logs to define geomechanical units and horizons which assist in characterising strata behaviour in coal mines
  • acoustic scanner images and interpreted data can be displayed in a variety of formats to visually convey the location and nature of geotechnical conditions
  • there is no discernible relationship between transit time contrast from sonic logs and height above mining in the intermediate and upper caving zones with respect to propensity for strata separation
  • the transit time contrast alone does not provide a reliable indication of potential parting planes that would result in strata separation during goafing
  • the sonic velocity can be used quantitatively in the immediate caving zone (up to about 7 times mining height) and a tentative relationship has been proposed for such application

Goafing behaviour above the immediate roof (approx 20m) is governed by a combination of factors, including bed thickness, strength homogeneity, and the juxtaposition of beds of contrasting character, and cannot be predicted solely on the basis of weak partings. However the identification of weak partings from the sonic log and weak beds and a high frequency of fractures or weak bedding planes from the scanner may be useful indicators of potential separation horizons.

Whilst the definition of goaf delamination horizons from the acoustic scanner or the sonic log has not been achieved by this project, considerable knowledge has been gained and demonstrated on the reliability, cost effectiveness, and contribution of these tools to the understanding and management of coal seam roof and goaf conditions.

To successfully define those horizons which contribute to the caving behaviour at any mine site significantly more data needs to be collected. The combination of suitably located and monitored extensometer installations in boreholes with acoustic scanner logs of the borehole will considerably assist the further understanding of this behaviour. The combination of various tools and methods may be required to ultimately predict the primary features which influence goaf formation.

Underground

Health and safety, productivity and environment initiatives.

Recently Completed Projects

C27039True Triaxial Strength Of Coal Measure Rocks And Its Impact On Roadway Stability And Coal Burst Assessment

Rocks in the ground are subject to a range of stresses. The stresses...

C3063Underground Vehicle Design Standards And Statutory Implications

The Australian underground diesel vehicle fleet has evolved since di...

C3064Conveyor Belting And Lagging Shear Characteristics - Drive Drum Slip

The primary aim of this project was to investigate the relationsh...

Underground

Open Cut

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

Recently Completed Projects

C26029Geological Controls On Fluorine And Phosphorus In Bowen Basin Coals

Increasing global restrictions on fluorine in product coal prompted ...

C28033Raw Ash To Yield Relationships

Correct outcomes in yield predictions for product ash from coal bore...

C27038Establishing Self-Sustaining And Recognisable Ecological Mine Rehabilitation

In recent years an increasing interest has been placed on mining ope...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C27064Dry Beneficiation Using FGX And X-Ray Sorters

Conventional dry processing methods engage a single beneficiation de...

C26010Multi-Sloped Screening Efficiency With Changing Strokes, Frequencies, Feed Solids And Feed Rates-Pilot Plant Study

Optimising multi-sloped screens is often described as an art and the...

C28059Impact Of Water Quality In Coal Handling And Preparations Plants

The objective of this project was to deliver a concise reference do...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Technical Market Support

Mine Site Greenhouse Gas Mitigation

Mitigating greenhouse gas emissions from the production of coal.

Recently Completed Projects

C23052Novel Stone Dust Looping Process For Ventilation Air Methane Abatement

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

C27054Optimisation Of A Thermal Flow Reversal Reactor For Ventilation Air Methane Mitigation

Ventilation air methane (VAM) generally accounts for 50-85% of the t...

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...

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