# Simulation of Rock Failure Cone Development Using a Modified Load-Transferring Anchor Design
###### Abstract
The use of conventional undercut anchors, however, poses significant operational challenges, primarily due to the necessity of employing specialized extraction equipment. Such equipment is typically heavy, bulky, and requires substantial working space for proper handling and maneuvering. As a result of a series of experimental studies, modifications to the anchor design have been proposed [34, 50], which also led to a fundamental change in the mechanism of load transfer from the anchor to the surrounding rock mass. As previously mentioned, one of the primary objectives of the authors is to determine the extent and parameters of the failure zone within a given rock mass, depending on the geometric features of the anchor, the mechanical properties of the rock medium, and the effective embedment depth. The essence of these investigations is illustrated in Figure 3 (based on [40,50]). Considering the limitations of the rock detachment method based on pulling out an anchor installed in accordance with standard anchoring procedures used for concrete, an alternative detachment process was carried out using a modified HDP-A type anchor. The modification involved detaching rock fragments by expanding the elements of the anchor near the bottom of the borehole, achieved by enabling the anchor's drive screw to thread into a conical head (e.g., [50]). During the detachment process, the torque applied to the drive screw was recorded. Based on the calibration of the measurement system, it was possible to determine the equivalent detachment force--analogous to the pull-out force used in conventional anchor-based detachment technology. The essence of this method is illustrated in Figure 4.  
Instead of relying on axial pull-out forces to detach a rock fragment--through extraction of the embedded anchor--a novel approach has been developed that utilizes radial expansion. In this method, the destructive force is applied by expanding the anchor components near the bottom of the borehole during the rotation of a central drive screw. This expansion induces high local stresses within the rock material, promoting controlled fracturing and detachment without requiring the full extraction of the anchor. One of the proposed solutions involving this modified detachment technology and anchor design is illustrated in Figure 5.  
An anchor equipped with an undercutting head (1), an expansion element (2), and a drive screw (3), when pre-installed in a borehole drilled into the rock mass, enables localized fracturing of the rock material near the borehole base (Figure 5) [62]. The cylindrical end of the drive screw is in direct contact with the bottom of the hole. As rotational motion is applied to the drive screw using a dedicated drive system, and the anchor head assembly is gradually displaced along the anchor's axis (with an incremental axial displacement denoted as \(\Delta\)Y in Figure 5, representing the imposed movement of components). This displacement induces progressive deformation of the surrounding rock and a corresponding increase in stress within the zone of influence around the undercutting head. Ultimately, this results in the porphyry initiation and propagation of a failure zone within the rock mass, typically forming a geometry resembling a breakout cone.