# The Bolt Anchorage Performance of Fractured Rock under a Freeze-Thaw Cycle Load
## 4 Analysis and Discussion
### Impact of Anchoring Conditions on Specim Strength  
Our anchoring methods are classified into three types based on the ratio of the length of the anchored section to the length of the borehole: end anchoring, extended anchoring, and full-length anchoring. Experimental comparisons were made between the strength and modulus of specimens with and without cracks, coupled with and without anchor rods, studying the supportive effect of full-length anchoring on the specimens. Statistical analyses were conducted on specimens subjected to different freeze-thaw cycles, as illustrated  
Figure 5: Box plots depicting the distribution of the strength and elastic modulus of specimens under different pre-existing fracture conditions: (**a**) strength in unbolted specimens, (**b**) strength in bolted specimens, (**c**) elastic modulus in unbolted specimens, (**d**) elastic modulus in bolted specimens.  
in Figure 5 and Table 7. From this analysis, the following conclusions can be drawn: (1) Under different prefabricated structural surface conditions, the influence of anchoring conditions on specimen strength varies significantly. Compared to unbolted specimens without fractures, the mean strength of unfractured bolted specimens decreases by 8.9%, while that of 45\({}^{\circ}\) fractured bolted specimens increases by 31.2%, and that of 90\({}^{\circ}\) fractured bolted specimens increases by 9.3%. Statistically, anchoring exhibits the most effective reinforcement for 45\({}^{\circ}\) fractured specimens. (2) Under different prefabricated structural surface conditions, the influence of anchoring conditions on a specimen's tangent modulus also exhibits significant variation. Compared to unbolted specimens without fractures, the mean tangent modulus of unfractured bolted specimens decreases by 13.7%, while that of 45\({}^{\circ}\) fractured bolted specimens increases by 26.8%, and that of 90\({}^{\circ}\) fractured bolted specimens increases by 14.2%.  
The reasons for these phenomena can be elucidated as follows: For unfractured specimens, the addition of a high-stiffness anchor, which is stiffer than the specimen's strength, leads to stress concentration around the anchor rod during failure, causing cracks to expand and weaken both their strength and stiffness (Figure 6). For 45\({}^{\circ}\) fractured specimens, sliding occurs along the pre-existing weak structural surface during failure; the anchor rod exerts tension and shear forces, providing an anchoring restraint in that direction. This simultaneously counteracts external forces in the sliding direction, thereby enhancing specimen strength. For 90\({}^{\circ}\) fractured specimens, due to the perpendicular orientation of the prefabricated structural surface to the end face, both the stress concentration and anchoring effects of the anchor influence the final failure of the specimen. The crack propagation shifts from predominantly extending from the pre-existing structural surface to jointly extending from around the anchor and the edge of the structural surface. The anchoring of the anchor controls crack propagation along the prefabricated structural surface, thereby enhancing its strength, while the stress concentration effect reduces the specimen's strength.  
Figure 6: _Cont._