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|Effective strata control, utilising fully encapsulated roof bolts, is dependent on the installed quality of the reinforcement elements. One mechanism by which fully encapsulated roof bolts may become less than fully effective is by gloving (glove fingering) and un-mixing of the resin. Following some small roof failures containing gloved bolts, investigations have been undertaken in some New Zealand coal mines to determine the extent of, and mechanisms involved in, the gloving of fully encapsulated roof bolts for a range of roof types and installation methods. Gloving, in this context, refers to the resin cartridge partially or completely enveloping a length of the bolt, typically with unmixed resin filler and catalyst/hardener remaining within the cartridge. Results have shown that gloving and un-mixing is a systematic and widespread phenomena, occurring across a range of resin and/or bolt manufacturers, and across a variety of roof types. Gloving was found in bolts installed using: hand held pneumatic and continuous miner mounted hydraulic methods, under run of mine (ROM) conditions by mine workers, and under controlled "best practice" conditions. The roofs bolts investigated are all 1800mm (6ft) long, and have shown that, on average, 485mm (-19") of the bolt length is gloved and/or unmixed. This equates to a 27 percent reduction in effective bolt length. The effected length of bolt is sufficient to impact on the load transfer/reinforcement capabilities of the bolt system, and hence impacts on the design assumptions and subsequent stability assessments. Furthermore, there is a direct relationship between the mechanism for the gloving of bolts and an increased occurrence of resin loss and reduction in encapsulations length in soft (less than 10 MPa) and/or highly fractured rock. Investigations have concentrated on developing an understanding of the mechanisms involved. This has been undertaken using both field installations and recovered bolts, as well as test bench trials. The mechanisms involved have been confirmed as being: the development of a pressure front as the bolt encounters the resin and is spun up the hole, which, in turn, leads to over-pressurisation and radial expansion of the resin cartridge, resulting in an increase in diameter of the plastic resin cartridge, which allows the bolt to be spun up into the cartridge without making sufficient contact to shred the cartridge or the hardener tube, resulting in an unmixed portion of resin.|
Additional chapters/articles from the SME-ICGCM book 22nd International Conference on Ground Control in Mining (ICGCM) 22nd
|Pillar Design and Roof Support for Controlling Longwall Head||Stress Analysis and Support Design for Longwall Mine-Through||The Utilisation of Numerical Modelling to Predict Water and||Longwall Roof Fall Prediction and Shield Support Recommendat||Comparison Of Multiple And Single Entry Roadways For Highly||Numerical Modeling Of Longwalls In Deep Coal Mines||The Characteristics Of Mining-Induced Fractures In Overlying||Design And Experience Of Total Extraction Room And Pillar Op||Using Site Case Histories Of Multiple Seam Coal Mining To Ad||Mining Method For Extracting An Eight Metre Coal Horizon Con||Stooping Low Safety Factor Pillars At Goedehoop Colliery||Modelling Of Pillar Stability In Room And Pillar Mines||Pillar Optimization For Initial Design And Retreat Recovery||Application Of RMT's Remote Reading Telltale System To||Rock Mechanics Study Of Lateral Destressing For The Advance-||New Tools For Roof Support Evaluation And Design||Considerations For Using Roof Monitors In Underground Limest||Mine Roof Geology Information System (MRGIS)||Imaging Ahead Of Mining With Radio Imaging Method (RIM-IV) I||Geophysics For The Detection Of Abandoned Mine Workings||Investigation Of Seam Thickness And Seam Splitting Within A||Determination Of Rock Strength Properties Using Geophysical||RQD from the Barrel to the Box: Weatherability May be a Bett||A probabilistic approach to ground support design in undergr||The Requirements of a Database to Store Geotechnical Data to||Variation of Horizontal Stresses and Strains in Mines in Bed||Geotechnical Planning Basis for the Optimization of Workings||Tensile roof failure arising from horizontal compressive str||Study of load transfer capacity of bolts using short encapsu||Intersection Stability and Tensioned Bolting||Premature Rock Bolt Failure Through Stress Corrosion Crackin||Short-encapsulation Pull Tests for Roof Bolt Evaluation at a||Field Test with Strain-gauged Friction Bolts at the Gold Hun||Directional Rock Bolt Pullout Tests as Index Tests for Estim||Eclipse Bolting System||The Application of Pre-tensioned Grouted Tendons at Harworth||Investigation into the Extent and Mechanisms of Gloving and||Developments in Improving the Standard of Installation and B||Development of Geotechnical Procedures for the Analysis of M||Recent Developments in the Use of Seismic Tomography in Long||Pumpable Roof Supports: Developing Design Criteria by Measur||Design Considerations of the Secondary Roof Support for Long||The Effect of Standing Support Stiffness on Primary and Seco||Numerical Modeling of the U1A Complex at the Nevada Test Sit||Rock Mechanics and the Analysis of Underground Mine Stabilit||A Study of Potential Fault Reactivation and Water Intrusion||The Elimination of Rock-fall Fatalities in Ontario Hardrock||Root Causes of Groundfall Related Incidents in U.S. Mining I||Analysis on the Dynamics of Mining Subsidence in Range of a||Mitigating Subsidence Influences on Residential Structures C||Influences of Longwall Subsidence on a Guyed Steel Tower - A||Surface Movement of Super-wide Longwall Panels Using Top-coa||New Approach to Evaluate the Stability of Yield Pillars||Experimental Study of Acoustic Emission Characteristics for|