Development of a New Yielding Rockbolt for Burst-prone and Convergence Ground

CIM MEMO 2010
John Oldsen,
Abstract With increasing mining depth and scale, there will be more and more industry requirements on yielding rock support for burst-prone ground and convergence ground. Jennmar conducted large scale research and development works to develop a technically reliable and cost effective yielding rock bolt. This paper introduces a new yielding rock support - Yield-Lok bolt.
The bolt is made of ¾ Grade 75 round bar with the minimum ultimate tensile strength of 16.7 ton. The bar is upset to specified dimensions at one end and encapsulated in an engineered Polymer Coating to achieve designed yielding performance under static or dynamic loading. The other end of the bar is threaded for tensioning with a nut.
In dynamic condition, the bolt is characterized by the designed yielding ability of 150 ~ 250mm of deflection at 8 ~ 10 ton loads for every 16.4kJ dynamic energy input, while the total yielding capability of the bolt is more than 500mm. Its performance characteristics are consistent through multiple and varying amplitude of impacts. In static condition, the bolt is characterized by yielding at the specified loads which is designed by modifying the upset diameter for convergence ground.
In this paper, the design criteria of the bolt and the principle of performance are described; the testing results are discussed; and the features and application of the bolt are presented.
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