# The Bolt Anchorage Performance of Fractured Rock under a Freeze-Thaw Cycle Load
## 4 Analysis and Discussion
### Analysis of Failure Modes and Crack Development
#### 4.5.2 Numerical Simulation Results  
The numerical simulation results align with the experimental findings, demonstrating a significant influence of anchor rods on the failure modes of specimens, as evidenced by the distribution of surface cracks and microcracks illustrated in Figure 12.  
1. In Figure 12a,b, for specimens without anchor rods and no pre-existing cracks, during uniaxial compression, oblique surface cracks and vertical surface cracks are observed, accompanied by spalling regions and occasional bulging spalling in the central area. Internal cracks are predominantly distributed across the inclined section of the breakthrough.
2. In Figure 12e,f, for specimens with a 45\({}^{\circ}\) pre-existing crack, surface cracks during uniaxial compression primarily occur on the inclined section, consistent with the pre-existing structural plane, with internal microcracks extending from the pre-existing structural plane.
3. Similarly, in Figure 12i,j, for specimens with a 90\({}^{\circ}\) pre-existing crack, surface oblique cracks and vertical cracks are observed during uniaxial compression, along with spalling regions, with a plethora of internal microcracks distributed around the pre-existing crack.
4. In Figure 12c,d, for specimens with anchor rods but no pre-existing cracks, during uniaxial compression, wing cracks extending from the stress concentration zones around the anchor rods are first observed, propagating outward as oblique cracks and vertical cracks. Additionally, localized spalling areas are present, with fracture surfaces intersecting with the stress concentration zones around the anchor rods.
5. Similarly, in Figure 12g,h, for specimens with anchor rods and a 45\({}^{\circ}\) pre-existing crack, the surface cracks during uniaxial compression primarily occur on the inclined section, consistent with the pre-existing structural plane, with internal microcracks  
Figure 12: Distribution of surface cracks and microcracks in specimens, with tension cracks in red and shear cracks in blue: (**a,b**) the unbolted specimen without fractures, (**c,d**) the unbolted specimen with a 45\({}^{\circ}\) fracture, (**e,f**) the unbolted specimen with a 90\({}^{\circ}\) fracture, (**g,h**) the bolted specimen without fractures, (**i,j**) the bolted specimen with a 45\({}^{\circ}\) fracture, (**k,l**) the bolted specimen with a 90\({}^{\circ}\) fracture.  
extending from both the pre-existing structural plane and stress concentration zones around the anchor rods. (6) In Figure 12k,l, for specimens with anchor rods and a 90\({}^{\circ}\) pre-existing crack, during uniaxial compression, wing cracks extending from the stress concentration zones around the anchor rods are observed, propagating outward as oblique cracks and vertical cracks, with localized spalling areas. Internal microcracks originate from both the pre-existing structural plane and stress concentration zones around the anchor rods.  
The numerical simulation results indicate a more pronounced occurrence of localized spalling in specimens without anchor rods, whereas specimens with anchor rods exhibit stress concentration phenomena around the anchor rods, leading to the formation of long cracks and breakthrough cracks. Internal microcracks predominantly initiate in the vicinity of the anchor rods and the pre-existing structural plane, with tension cracks outnumbering shear cracks significantly.