# Pull-Out Test and Mechanical Properties Analysis Based on Intelligent Bolt and Internet of Things
## 4 Test Result Analysis
### Distribution Law of Axial Force and Friction Resistance of Bolt
The axial force is used for the whole section of the anchorage body. The axial forces in the bolt with an anchorage length of 20 m are measured as 302 kN, 60 kN, and 0.17 kN, respectively. It is observed that the axial force is primarily concentrated in the first half of the anchorage section. By analyzing the above reasons, from the perspective of key sliding behavior, the first half of the anchor rod bears the largest tension, and the shear stress on the interface between the anchor rod and the rock and soil mass is also the largest. When the shear stress exceeds the bond strength or friction strength of the interface, the bond slip phenomenon will occur. Once the key slip occurs, the cohesion and friction between the bolt and the rock and soil will decrease sharply. The effect of transferring the axial force to the rock and soil mass by these forces is greatly weakened, so that the axial force cannot continue to be effectively transmitted to the back half, and can only decay rapidly in the key slip area. From the perspective of stress redistribution, when the rock and soil mass in the first half of the bolt reaches its bearing limit, the stress will be redistributed. The force originally borne by the first half of the rock and soil mass needs to be transferred to the second half of the rock and soil mass. However, the latter half of the rock and soil mass bears less stress in the initial stage, and the exertion of its bearing capacity requires a certain deformation process. At the moment of stress redistribution, the axial force of the first half will decrease rapidly, and the axial force of the latter half will increase relatively slowly. This results in the phenomenon that the axial force attenuates the most in the first half. It can be clearly seen from Figure 10 that the friction resistance is unevenly distributed along the length of the anchorage body, and the linear distribution trend is not obvious. Specifically, the friction resistance peaks at 0.75 m from the front end of the anchorage body and then gradually decreases as the anchorage depth increases, resulting in a single-peakcurve. With the increase in the tension at the end of the rod, the peak friction resistance moves downward when the anchor length is 10 m and the tension value is 140 kN. When the anchorage length is 20 m, the peak friction resistance moves downward when the tension value is 140 kN, 260 kN and 300 kN. This is because the peak friction resistance precedes the convex section of the plastic deformation stage of the anchor body, which corresponds to the axial force of the anchor rod. Following the peak friction resistance, the elastic stage ensues, where there is a gradual attenuation along the depth direction as the rod end tension increases, aligning with the axial force distribution law. When comparing the friction resistance of bolts with varying anchorage lengths under ultimate pull-out bearing capacity, it is observed that the peak friction resistance remains largely consistent. However, as the depth increases, bolts with longer anchorage lengths exhibit lower friction resistance and a more uneven distribution curve. Taking the average friction resistance of the smooth section of the curve, the average friction resistance of the bolt with an anchorage length of 10 m is 57 kN, while the average friction resistance of the bolt with an anchorage length of 20 m is 30.5 kN, which is reduced by 46.4%. Based on the axial force transfer law of the bolt and the analysis of frictional resistance, it is evident that the strength of the first half of the bolt should be increased when using long bolts to support a slope.