# The Bolt Anchorage Performance of Fractured Rock under a Freeze-Thaw Cycle Load
## 4 Analysis and Discussion
### Analysis of Failure Modes and Crack Development  
#### 4.5.1 Laboratory Test Results  
1. As shown in Figure 11(a-1), the specimen without bolts or prefabricated fractures exhibits a failure mode characterized by local spalling and overall brittle irregular shear. Fractures initiate from the surface in the form of local tensile-induced vertical wing fractures. As these fractures propagate vertically, adjacent fracture edges intersect to form oblique fractures and even lateral fractures with bulging, some of which progress inward, leading to partial spalling. As illustrated in Figure 11(a-2), the oblique fractures and vertical fractures that have not yet resulted in spalling continue to propagate inward, with larger fractures penetrating the specimen upon failure. 2. The specimen with bolts but without prefabricated fractures displays a failure mode characterized by local spalling and brittle shear failure developing around the bolt-induced stress concentration zone. As shown in Figure 11(b-1), fractures initiate from the end face and around the bolt-induced stress concentration zone, manifesting as local tensile-induced vertical or oblique wing fractures. Some surface fractures intersect and propagate inward, potentially resulting in spalling. As depicted in Figure 11(b-2), the failure surface typically consists of fractures that independently or mutually communicate through vertical-oblique cracks, oblique-oblique cracks, or Y-shaped cracks formed by the bolt. 3. In Figure 11(c-1), the specimen with a 45\({}^{\circ}\) prefabricated fracture but without bolts exhibits a failure mode characterized by brittle sliding along the prefabricated structural surface. Prior to failure, the specimen also exhibits local tensile-induced vertical wing fractures, some of which have the opportunity to form spalling zones or similar spalling-like morphologies before complete failure. As shown in Figure 11(c-2), near failure, certain parts of the specimen's surface projected along the long axis of the prefabricated fracture initiate shear fractures, which subsequently extend to form an entire oblique fracture surface, resulting in complete internal sliding along the prefabricated structural surface upon failure. 4. The specimen with a 45\({}^{\circ}\) prefabricated fracture and bolts exhibits a failure mode characterized by brittle sliding along the prefabricated structural surface. This mode includes the development of vertical fractures along the end face, vertical fractures leading to spalling, and oblique fractures induced by the stress concentration zones around the bolt (as shown in Figure 11(d-1,d-2)). Additionally, there are fractures expanding outward from the prefabricated structural surface, with some fractures overlapping and interconnecting. During the specimen's sliding along the prefabricated structural surface, the bolt anchorage restricts movement. As failure occurs, fractures propagate outward around the bolt, and once the fractures reach a critical size and quantity, the anchorage effect fails, leading to specimen failure. Figure 10: The stress–strain curves obtained from experimental observations and numerical simulations. 5. The specimen with a 90\({}^{\circ}\) prefabricated fracture but without bolts exhibits a failure mode characterized by local spalling and overall brittle multi-angle shear. During the fracture development stage, local tensile-induced vertical wing fractures are observed. As these fractures propagate vertically, adjacent fracture edges intersect to form oblique fractures (as shown in Figure 11(e-1)), with some specimens also exhibiting lateral fractures and bulging. The failure mode includes one type of destruction along the prefabricated structural surface and its extensions, and another type of oblique brittle shear failure not along the prefabricated structural surface, as illustrated in Figure 11(e-2). 6.