Experimental Verification of Standard Recommendations for Estimating the Load-Carrying Capacity of Undercut Anchors in Rock Material

Abstract

The recommendations put forward in the International Standards for anchorage in concrete concerning the assessment of the load-carrying capacity of anchors (the pull-out force) embedded in natural rock material were verified. Regarding the predicted extent of surface failure we have shown, in earlier studies, substantial discrepancies between the strength test results for anchorages in the rock mass and the established standard recommendations for anchorages in concrete. As regards the industrial practice and the goals of the reported project, simplified calculation procedures that will facilitate the selection of optimal configurations for the layout of anchor holes, while being computationally effective and applicable under the industry-specific conditions are sought.

Influence of the Undercut Anchor Head Angle on the Propagation of the Failure Zone of the Rock Medium

“…This was demonstrated by detailed numerical analyses as well as field investigations by the authors of the study. The present study complements and extends previous analyses conducted by the team of authors of the study, especially [ 31 , 33 , 35 , 36 , 37 , 39 ].…”

“…Rock failure under the action of an undercutting anchor is a highly complex problem. Unlike in concrete, disturbances in the internal structure of rocks cause a significant scattering of results obtained during the determination of physical and mechanical parameters of the base material and in anchor pull-out tests [31,33,39]. Therefore, the main premise of the research conducted by members of the research team was to determine the tendency of changes in the process of rock destruction, which can be observed during changing physical and mechanical parameters of rocks, parameters of execution of the anchor pullout process and changes of design parameters of the undercutting head.…”

“…In previously published studies [ 31 , 33 ], the radius of the support arrangement (R) of the anchor pull-out device (with three adjustable supports) was altered in the range of 300–390 mm (as required). The depth h ef was ~50–140 mm.…”

“…This technology is envisaged as an alternative in specific areas of mining activity, e.g., where other mining techniques (the use of explosives or mechanical mining, e.g., shearers) are not possible. Due to the heterogeneity of the internal rock structure, there are certain deviations from the current description of the phenomena of failure of concrete structures, both in terms of the value of the anchor pull-out forces and the extent of the potential failure zone [ 33 ].…”

The Influence of the Physical-Mechanical Parameters of Rock on the Extent of the Initial Failure Zone under the Action of an Undercut Anchor

“…Due to the limited knowledge in the field of pull-out of anchors installed in rock media, research has been undertaken (e.g., [17][18][19]) to find out whether previous findings on the propagation of concrete failure under the action of undercut anchors can be transposed to processes occurring in natural rock media. In comparison to concrete, such media have a complex internal structure (e.g., layering), as well as more varied physical and mechanical parameters, related, among other things, to the history of their formation or location in the rock mass.…”