Abstract
An objective of this study was to investigate the group effect in rock cone failure occurring in pull-out with the use of 3D finite element analysis. At present, undercut anchors are typically applied as structural fasteners of steel elements in concrete buildings; however, new areas for their use are being explored. The reported study set out to evaluate the use of undercut anchors in special-purpose rock mining, e.g., in mining rescue operations. In such emergencies, mechanical mining may prove impossible, whereas the use of explosives is even prohibited. Although manual methods could be considered, their effectiveness is hard to assess. Prior to considering the use of undercut anchors in mining, several aspects must essentially be determined: The mechanics of cone failure, including the extent of surface failure and the values of the pull-out force of the anchor for a given rock mass relative to the anchor system, the embedment depth, or the rock strength parameters. These factors may be investigated successfully using finite element analysis, the results of which are presented in the study.
Highlights
Undercut anchors are primarily considered in use as fasteners in steel elements of concrete structures
The currently accepted empirical models describing the mechanism of the breakout prism formation have been developed from the numerous experimental studies
Based on linear elastic fracture mechanics (LEFM), Eligehausen and Savade [13] developed an analytical/theoretical model, which enables the potential anchor load capacity to be determined from the following relationship:
Summary
Undercut anchors are primarily considered in use as fasteners in steel elements of concrete structures. Based on linear elastic fracture mechanics (LEFM), Eligehausen and Savade [13] developed an analytical/theoretical model, which enables the potential anchor load capacity to be determined from the following relationship: 0.5 a FEG f = a1 EG f h1.5 f (3) In this model, the load capacity (anchor pull-out strength) FEGF (N) is a function of the calibration factor a1 , the anchoring depth hef (mm) in the exponent 1.5, the modulus of elasticity of concrete E, and the fracture energy of concrete GF. 3D FEM systems are highly suitable for the analysis of breakout prism formation (surface delamination) and for modelling how changes in the effective embedment depth or the distance between anchors, in two-anchor and multiple-anchor systems, affect the shape of the breakout cone [15] This mechanism is essential from the perspective of fastening and from the viewpoint of different applications of breakout technology. Equipped with the theoretical models and data, engineers are able to drill holes for anchors that ensure a maximum breakout prism volume in given geological and technological conditions, which translates to substantial progress in the removal of base material
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