Effect of Undercut Bolt Anchor Depth on Failure Cone Geometry: A Numerical FEM Analysis and Experimental Verification

This study examined the influence of the effective embedment depth h_ef of undercut anchors and the diameter of their heads on the formation of the so-called cone failure angle α. Cone failure formation during simulated anchor pull-out tests was analyzed numerically using the Finite Element Method (FEM) with the ABAQUS software and the XFEM algorithm. The analysis was conducted for three sizes of undercut anchor heads and four embedment depths. The numerical analysis results were compared with field test results obtained during pull-out tests of anchors installed in a rock medium (sandstone). Good agreement was observed between the numerical and field test results. The results of the numerical study are highly consistent with those obtained during the field survey. Moreover, they align closely with findings from previous numerical studies conducted by members of the research team, as presented in earlier publications. For the assumed simulation and field test conditions (sedimentary rocks, gray sandstone), no clear correlation was found between the embedment depth or the anchor head diameter and the value of the cone failure angle in the initial phase of the failure zone development. This result contrasts with certain findings reported in the literature. Many existing studies on anchor bolts focus on material properties or load-bearing capacity, but lack an in-depth analysis of how anchor depth influences the geometry of the failure cone. This research addresses that gap, providing valuable insights with practical implications for design codes and safety evaluations.