# Simulation of Rock Failure Cone Development Using a Modified Load-Transferring Anchor Design
## 3 Results and Discussion
Most significantly, the two-stage crack propagation process, characterized by initiation beneath the tip of the drive screw and subsequent progression toward the free surface, deviates from the uniform failure trajectories assumed in traditional models. This divergence underscores the necessity of extending existing theoretical frameworks to incorporate alternative fracture propagation mechanisms, especially in cases involving non-standard anchor geometries and atypical loading modes. Such developments are essential for the effective design and optimization of rock excavation systems, particularly under mining conditions where conventional assumptions may no longer hold. A major limitation of the technology based on the extraction of undercut anchors was the bulky size of the equipment required to pull out the anchor along with the detached rock fragment. This significantly restricted the applicability of the proposed method in underground mining, particularly due to spatial constraints in confined working environments. In contrast, the newly proposed anchor design for rock fracturing does not suffer from such limitations. The results of the conducted analyses indicate high potential for the proposed solution in engineering applications, especially in scenarios where the use of explosives is prohibited or where space is limited--such as mine rescue operations, microtunneling, or the restoration of rock-cut historical structures. The compact design of the anchor, which does not require heavy activation equipment, offers an effective alternative to traditional mechanical excavation technologies. Furthermore, the system may also be applicable in military and civil operations involving controlled rock mass fragmentation, where precision, safety, and portability are of critical importance. The presented numerical analyses revealed a high sensitivity of the applied rock-anchor interaction model to several key factors, including:  
* The mesh density in critical regions of the model;
* The element size (edge length of finite elements);
* The radial clearance between the cylindrical borehole wall and the cylindrical surface of the anchor. These parameters were found to have a particularly strong influence on the location of crack initiation under the action of the anchor head, as illustrated in Figures 12 and 13. Small variations in these factors resulted in noticeable changes in the stress distribution and  
Figure 13: Bimodal crack development under the action of the detachment anchor: 1—diminishing primary crack; 2—secondary crack leading to the detachment of a larger rock fragment. -fracture trajectory, emphasizing the need for precise meshing and geometrical definitions in future modeling efforts. Although the present model employed typical mechanical parameters for sandstone, it is important to emphasize that the physical and mechanical properties of natural rocks can exhibit significant variability, resulting from factors such as porosity, stratification, and moisture content. Therefore, it is advisable to conduct a series of parametric studies to evaluate the influence of key factors--such as tensile strength (\(f_{t}\)), Young's modulus (\(E\)), and fracture energy (\(G_{t}\))--on the shape and extent of the failure zone. Such analyses would contribute to the development of a more robust and generalized predictive model, capable of accounting for the variability of geotechnical conditions and enhancing the reliability of anchor-based rock detachment technologies across diverse geological environments. The use of a \"penalty\" contact model with an assumed friction coefficient \(\mu=0.2\) had a significant impact on the localization of stress concentration zones near the tip of the drive screw and the anchor head. This parameter plays a critical role in determining the crack initiation trajectory and can lead to substantial variations in the resulting failure pattern.