SCT Operations (Strata Control Technology)
  • Winton Gale

Welcome to SCT's own publications library which contains a collection of recent publications and other resources with reliable research about our technology. 

  • Experience in the Application of Computer Modelling to Coal Mine Roadway Design in Weak Rock - Winton Gale

    A summary of the weak rock failure process is presented to demonstrate the application of computer modelling to coal mine roadway design. The weak rock failure mechanism was chosen because its discovery required a design tool (modelling) that was not bound by a preconception of the results. Modelling was used to decode the relative influence of the geological and geotechnical factors.

    It is emphasised that computer simulation techniques are best applied in a practical sense if accompanied by field measurement and observation. The field measurements are used as both a means of validating the initial model and to confirm that actual events are within design expectation. Experience-in-the-Application-of-Computer-Modelling-to-Coal-Mine-Roadway-Design-in-Weak-Rock-W.Gale.pdf1.2 MB
  • Experience in Modelling Longwall Support Behaviour - Winton Gale

    Recent advances in computer simulations of strata caving mechanisms and the response of longwall supports to strata behaviour has allowed much better understanding of longwall support requirements. The computational method allows the simulation of longwall support behaviour under a wide range of geological conditions with emphasis on comparing different support geometries and support loading conditions. This paper presents results of the computational trials to simulate various longwall support geometries including the comparison of the two leg and the four leg support options, the premature caving of strata at the canopy rear and its influence on roof falls at the longwall face.

    The rock fracture distribution and caving characteristics of a wide range of strata geologies has a significant influence on the longwall support behaviour. Underground measurements and computer simulations were undertaken to investigate the caving characteristics of strata and some of the common problems typically encountered at the longwall face. The computer simulations highlight the importance of the longwall support geometry and location of the applied roof loads to minimise potential problems leading to major roof falls at the longwall face. Experience-in-Modelling-Longwall-Support-Behaviour-W.Gale.pdf1.9 MB
  • The Implications of Chain Pillar Geometries for Chinese Coal Mines - Winton Gale

    The retreating longwall method using single entry gateroads is the predominant coal mining method in Chinese underground mines. Leaving only a very small pillar between adjacent panels has become the normal longwall mining practice.

    It has been found that, rock bolting can improve the roadway conditions, however the general stability against roadway collapse will be determined by the adjacent goaf fracture geometry and chain pillar strength. With the increasing percentage of gateroads supported solely by rock bolting, there is now a key requirement to reexamine chain pillar design issues and the implications for gateroad support practice in China.

    This paper describes the current industry practices and experiences with chain pillar design in China and attempts to define some of the chain pillar design implications for current Chinese practice. Considerations for future design of chain pillars with regard to roadway support practices and overall gateroad stability against major roadway collapses induced by re-mobilisation of adjacent goaf are provided. The-Implications-of-Chain-Pillar-Geometries-for-Chinese-Coal-Mines-W.Gale.pdf1 MB
  • Rock Damage Characterisation from Microseismic Monitoring - Winton Gale

    This paper outlines the concepts used to correlate rock failure with microseismic events and presents examples of microseismic monitoring together with associated computer modelling of the rock failure. This study is motivated by the need to develop improved ways to reduce ground control hazards in underground mining. Toward this end we present and compare results from numerical modelling and microseismic monitoring studies conducted at several different mine sites. Emphasis is on integrating results obtained with these tools to characterize, and thus increase our understanding of, important mine deformation processes. The ultimate goal is to use this knowledge to design mine structures, and develop mitigation
    measures, that minimize specific ground control hazards. Rock-Damage-Characterisation-from-Microseismic-Monitoring-W.Gale.pdf700 KB
  • Stress Conditions and Failure Mechanics Related to Coal Pillar Strength - Winton Gale

    The aim of this paper is to discuss the rock mechanics issues which can influence the strength of pillars in coal mines. The paper utilises stress change monitoring results, micro seismic monitoring results and computer modelling to assess the stress history about a chain pillar. The implications and fracture modes developed are discussed, with the outcome being that chain pillar strength can be significantly reduced by the stress path and changes in boundary conditions to the pillar when longwall extraction occurs. It is envisaged that this effect is contained in measured and empirical data bases, however it is important to recognise the stress path process when applying results to various site conditions and mine layouts. Stress-Conditions-and-Failure-Mechanics-Related-to-Coal-Pillar-Strength-W.Gale.pdf524 KB
  • Estimation of the Hydraulic Conductivity of the Overburden above Longwall Panels in Coal Mines - Winton Gale

    The aim of this paper is to summarise and update the results of Australian Coal Association Research Project (ACARP) Report C13013 which relate to water inflows into a mine which occur through the overburden above and adjacent to longwall panels. The study assessed available data of inflows into underground coal mines and utilised computer simulation of water flow through fracture networks. The study concluded that flow into mines is typically via an interconnected network of pre-existing and mining induced fractures. The height above the coal seam that mining induced fractures extend is typically related to the width of the panel and the thickness of the coal extracted. However the potential for those fractures to form a connected network which can facilitate flow, is related to the amount of subsidence and the depth of mining. The study compares model simulations with measured data and provides guidelines to estimate the average hydraulic conductivity of the overburden above extracted longwall panels in Australia. Estimation-of-the-Hydraulic-Conductivity-of-the-Overburden-above-Longwall-Panels-in-Coal-Mines-W.Gale.pdf979 KB
  • Experience of Field Measurement and Computer Simulation Methods for Pillar Design - Winton Gale

    Coal pillar design has been based on generalised formulae of the strength of the coal in a pillar and experience in localised situations. Stress measurements above and in coal pillars indicate that the actual strength and deformation of pillars varies much more than predicted by formulae. This variation is due to failure of strata surrounding coal. The pillar strength and deformation of the adjacent roadways is a function of failure in the coal and the strata about the coal. When the pillar is viewed as a system in which failure also occurs in the strata, rather than the coal only, the wide range of pillar strength characteristics found in the UK, USA, South Africa, Australia, China, Japan and other countries are simply variation due to different strata-coal combinations and not different coal strengths.

    This paper presents the measured range of pillar strength characteristics and explains the reasons. Methods to design pillar layouts with regard to the potential strength variations due to the strata strength characteristics surrounding the seam are presented.

    Experience-of-Field-Measurement-and-Computer-Simulation-Methods-for-Pillar-Design-W.Gale.pdf513 KB
  • Geotechnical Issues for Multi Seam Longwall Panels - Winton Gale

    The design of longwall panel layout for multi-seam mining is a very important issue for mining districts where economic seams are in close proximity. Layout options for longwall panels relate to variations of vertical superposition maintaining a constant chain pillar location or offsetting the panels and undermining overlying chain pillars. A design process to assess the various layout options is discussed, together with the relevant issues related to chain pillar strength, subsidence and induced permeability within the overburden. The design process has utilised computer modelling of the caving process together with international experience to asses the various layouts.

    The paper will discuss these issues with regard to a site study undertaken in the Hunter Valley under ACARP funding. Geotechnical-Issues-for-Multi-Seam-Longwall-Panels-W.Gale.pdf6.9 MB
  • Geological Issues Relating to Coal Pillar Design - Winton Gale

    The strength characteristics of coal pillars have been studied by many workers and the subject is well discussed in the literature (for example. Salamon and Monro, 1967; Wilson, 1972: Hustrulid, 1976). A range of strength relationships have been derived from four main sources:
    - Laboratory Strength measurements on different-sized coal block specimens;
    - Empirical relationships from observations of failed and unfailed pillars;
    - A theoretical fit of statistical data and observations; and
    - Theoretical extrapolation of the vertical stress buildup from the ribside toward the pillar centre, to define the load capacity of a pillar.

    Geological-Issues-Relating-to-Coal-Pillar-Design-W.Gale.pdf240 KB
  • Performance of Roof Support Under High Stress in a US Coal Mine - Winton Gale

    The National Institute for Occupational Safety and Health's (NIOSH) Pittsburgh Research Laboratory (PRL), RAG Pennsylvania and Strata Control Technologies of Australia have collaborated to conduct an extensive study of roof bolt strata interaction at the Emerald mine in Southwestern Pennsylvania. The primary goal of the project was to obtain detailed data on the interaction between the mine roof and the support elements for use in modeling studies. The study site was a longwall tailgate subjected to high horizontal stress. Three arrays of instruments were installed at the site, one in the tailgate entry and two in an adjacent crosscut. Pumpable concrete cribs were present in the tailgate array, and cable bolts were installed in one of the crosscut arrays. The instruments included mechanical and sonic extensometers for measuring roof movement, instrumented roof bolts, and three-dimensional roof stress cells. The study was ultimately successful in determining the magnitude of the horizontal stress concentration, the height of roof failure and the roof failure sequence, and the loading history of the primary roof supports. Performance-of-Roof-Support-Under-High-Stress-in-a-US-Coal-Mine-W.Gale.pdf175 KB
  • Rock Fracture Caving and Interaction of Face Supports Under Different Geological Environments. Experience from Australian Coal Mines - Winton Gale

    This paper is presents a summary of recent investigations into fracture and caving about longwall panels. The results of these investigations indicate that rock failure initiates well ahead of the longwall face. Rock fracture typically forms in response failure through the material and bedding planes. Tensile fractures also form in massive units. These fracture patterns typically create a fracture network which determines the caving characteristics encountered at the faceline. The action of longwall face supports under such conditions is to maintain confinement to the fractured ground and develop a consistent caving line. The confinement developed above the canopy under these conditions can be variable on a shear by shear basis and the operational face support procedures play an important role in stability about the face area. Rock-Fracture-Caving-and-Interaction-of-Face-Supports-Under-Different-Geological-Environments.-Experience-from-Australian-Coal-Mines-W-Gale.pdf2 MB
  • Investigation into Abnormal Increased Subsidence above Longwall Panels at Tahmoor Colliery NSW - Winton Gale

    Tahmoor Colliery, located in the Southern Coalfield of NSW, has been in operation for over 30 years. Longwall extraction of 23 successive longwall panels has occurred with subsidence occurring within predictions and resultant impacts to natural and built environments occurring to expectations.

    Subsidence over a recent longwall panel of approximately twice that previously measured occurred at Tahmoor Colliery. An investigation of the potential causes was conducted using computer modelling together with hydrological characterisation and detailed geotechnical characterisation of the strata.

    The abnormal subsidence was found to be consistent with localised weathering of joint and bedding planes above a depressed water table adjacent to an incised gorge. The study showed that other factors such as variation in stress field, joint zones, variation in rock strength and topographic factors did not sufficiently induce the abnormal subsidence.

    The results have significant implications to subsidence prediction in areas which may be prone to the phenomenon found at Tahmoor. Key indicators of the potential for this form of abnormal subsidence are presented. Investigation-into-Abnormal-Increased-Subsidence-above-Longwall-Panels-at-Tahmoor-Colliery-NSW-W.Gale.pdf2.4 MB
  • Reinforcement Design of Cataract Water Tunnel to withstand Longwall Subsidence - Winton Gale

    This paper presents the procedures followed in the design of the reinforcement system for Cataract Tunnel. The Tunnel is a 19th century unlined tunnel under which a series of longwalls will be extracted at Appin Colliery. Based on the prediction of subsidence
    levels, three dimensional stress analyses were conducted to investigate the range of additional stresses which were likely to be induced around the tunnel. The impact of the induced stresses on the tunnel were then analysed in detail and a reinforcement system designed.

    It should be noted that, as in most geotechnical situations it was not possible to define all the relevant variables. Stress variations outside those used in this analysis are possible. In recognition of this and the uncertainty of the actual stress redistributions, the design has been used as the basis for a minimum support pattern. It is envisaged that this may be supplemented by additional reinforcement such as additional bolts or cable tendons as determined by a planned program of monitoring and observation. Reinforcement-Design-of-Cataract-Water-Tunnel-to-withstand-Longwall-Subsidence-W.Gale.pdf446 KB
  • Prediction of strata caving characteristics and its impact on longwall operation - Winton Gale

    Recent advances in computer simulation together with field measurements of caving and microseismic activity about longwall panels, has allowed a much better understanding of the caving process and the variability due to geology. The joint research between SCT Operations and CSIRO Division of Exploration and Mining has initiated new methods of computational modelling predicting various caving patterns and strata failure far ahead of the longwall face. This work was validated by field measurements of caving and microseismic activity at the longwall face.

    The rock fracture distribution and the caving characteristics of a range of strata sections have been simulated by computer methods. Validation studies of the method were addressed together with case studies. The interaction of caving with support convergence and face control is presented. The method allows the simulation of longwall support behaviour under various geological conditions. The system also allows a prediction of the monitoring data, which is best suited to give an early warning of weighting events or signal various key caving characteristics. Prediction-of-strata-caving-characteristics-and-its-impact-on-longwall-operation-Winton-Gale-1998.pdf2.9 MB
  • Investigation into Temporary Roof Support Principles - Winton Gale

    An investigation was undertaken in regard to Temporary Roof Support (TRS) systems incorporated into miner bolters. Two and three dimensional modelling was utilised to document the effects a TRS system may have on the surrounding underground environment. TRS systems were found to have little if any effect on strata stability about a simulated roadway but are considered capable of providing protection against minor roof falls where the operator is within the defined protection zone. Each system requires the combination of mesh, bolts and support points to provide a protective zone to the operators. In difficult conditions there is no substitute for bolting as close to the face as possible and the concept of a zone of influence about a support point, as indicated by industry guidelines is not considered as a suitable protection zone. Investigation-into-Temporary-Roof-Support-Principles-W.Gale.pdf1.8 MB
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