Welcome to SCT's own publications library which contains a collection of recent publications and other resources with reliable research about our technology.
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The Implications of Chain Pillar Geometries for Chinese Coal Mines - Winton Gale
Published Aug, 2017The 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 -
Investigation Into the Extent and Mechanisms of Gloving and Un mixed Resin in Fully Encapsulated Roof Bolts - Stuart MacGregor
Published Aug, 2017Effective strata control, utilising fully encapsulated roof bolts is dependent on the installed quality of the reinforcement elements. One mechanism by which roof bolts may become less than fully efficient is by glove fingering (gloving) and un-mixing of the resin. Following a routine installed bolt quality audit and some small roof failures containing gloved bolts, a work programme was initiated to determine the extent of the gloving and un-mixing problem and to develop an understanding of mechanisms involved. Results have shown that gloving and un-mixing is a systematic and widespread pheno mena, occurring across the range of resin and/or bolt manufacturers, and in a variety of roof types. Gloving was found in bolts installed using either hand held pneumatic or continuous miner mounted hydraulic bolting rigs, under run of mine (ROM) condition s by operators, and under controlled manufactures “best practice” conditions.
The mechanisms involved have been confirmed as being the development of a pressure front as the bolt encounters the resin cartridge and is spun up the hole, which in turn, leads to over -pressurisation and radial expansion of the resin cartridge. The result is an increase in the diameter of the plastic cartridge. Allowing the bolt to be spun up inside the cartridge without making sufficient contact to shred the cartridge or the hardener envelope, typically resulting in a portion of the cartridge enveloping the bolt and unmixed resin mastic and catalyst.
Once the mechanisms involved and extent of the problem became clear, further research was undertaken to assess alternative bolt profiles and modifications in an effort to minimise and/or eliminate the gloving and unmixing phenomenon. Research has been undertaken using recovered bolts from various mine sites, as well as test bench trials and the quantification of the loading characteristics of gloved bolts using strain gauge roof bolts.
To understand the impacts of gloved and un-mixed bolts on roof control, failure pathways and reinforcement requirements a FLAC 2D numerical simulation was undertaken, with the results being incorporated into the strata management plan for a particular operation. Laboratory data has been collected and analysed to assess magnitudes of resin pressure as the bolt encounters the cartridge1 and the effects of gloving and un-mixing on the load transfer characteristics of the resin bolt system. Investigation-Into-the-Extent-and-Mechanisms-of-Gloving-and-Un-mixed-Resin-in-Fully-Encapsulated-Roof-Bolts-S.MacGregor.pdf502 KB -
Geotechnical Issues for Multi Seam Longwall Panels - Winton Gale
Published Sep, 2017The 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
Published Sep, 2017The 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
Published Sep, 2017The 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 -
Reinforcement Design of Cataract Water Tunnel to withstand Longwall Subsidence - Winton Gale
Published Nov, 2017This 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
Published Feb, 1998Recent 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