Computer Simulation of Ground Behaviour and Rock Bolt Interaction at Emerald Mine - Winton Gale - Published 2004A collaborative project between RAG Emerald Mine, NIOSH, and SCT Operations was conducted to investigate ground behaviour, reinforcement performance, and stress redistribution in a coal mine entry subjected to a severe horizontal stress concentration. Field measurements indicated that the stresses applied to the study site nearly doubled during longwall mining, resulting in roof deformations extending to a height of 4.8 m (16 ft) above the entry.
This paper focuses on the computer simulation that was undertaken to provide more insight into the roof behaviour and rock bolt interaction during mining. The model’s input rock properties were derived from extensive laboratory testing, and the model itself simulated a broad range of failure mechanisms. The effects of different bolt patterns on roadway behaviour were evaluated. Comparison between the model results and the field measurements indicated that that the model effectively simulated the critical elements of the actual roadway’s behaviour. With the confidence gained, the model was used as a baseline for additional simulations that evaluated the expected performance of alternative roof support systems. The study will also provide a benchmark data set for future applications of numerical modelling to U.S. coal underground mining. Computer-Simulation-of-Ground-Behaviour-and-Rock-Bolt-Interaction-at-Emerald-Mine-Winton-Gale.pdf697 KB
Statistical Analysis of Undeground Stress Measurements in Australian Coal Mines - Winton Gale - Ken MillsThis paper presents a summary of 235 underground stress measurements conducted in the virgin ground of NSW and Queensland mines. The main objective of this study is to analyse the statistical information from the measurements that are relevant to strata control and mine planning with a view to estimate the risk involved with strata failure.
Major findings include the statistical increase of maximum horizontal stress with depth in Queensland and NSW mines, a comparison of normalised lateral stress magnitudes and measurements in rock of a different stiffness, ‘Tectonic Factor’ concept, and maximum lateral stresses and their directions in NSW and Queensland coalfields. These findings can provide a valuable benchmark for mine planning and strata control with potential savings in mine operating costs. Statistical-Analysis-of-Underground-Stress-Measurements-in-Australian-Coal-Mines-W.Gale-K.Mills.pdf2 MB
Stress Conditions and Failure Mechanics Related to Coal Pillar Strength - Winton GaleThe 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
Experience of Field Measurement and Computer Simulation Methods for Pillar Design - Winton GaleCoal 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.
Geological Issues Relating to Coal Pillar Design - Winton GaleThe 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.
Performance of Roof Support Under High Stress in a US Coal Mine - Winton GaleThe 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