# 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  
By monitoring the steel bar stress gauges during the pull-out test, the axial force for each measured section under various levels of tensile load is calculated, as illustrated in Figure 9, and the distribution of friction resistance is shown in Figure 10. Since the stress  
Figure 8: Anchorage length-ultimate pull-out bearing capacity curve. distribution of anchors with anchorage lengths of 20 m and 30 m is similar, anchors with anchorage lengths of 10 m and 20 m are selected for stress analysis. As shown in Figure 9, the axial force in the bolt gradually increases with the increase in tension at the bolt end. However, it decreases along the direction of the anchorage depth, with the greatest attenuation occurring in the first half of the bolt body. When the tension at the end of the rod is less than the elastic ultimate load value (180 kN when the anchorage length is 10 m, and 220 kN when the anchorage length is 20 m), the curve is concave; as the tension at the end of the rod continues to increase, the anchorage body enters the strengthening stage. The curve is obviously convex at the end of the anchorage body. For a bolt with an anchorage length of 20 m, when the tension at the end of the bolt reaches its ultimate pull-out bearing capacity, the curve becomes a smooth straight line. The axial force in the bolt approaches its maximum value, which is approximately one third of the tension at the end of the bolt. Figure 10: Friction resistance distribution curve. (**a**) Anchorage length 10 m; (**b**) Anchorage length 20 m.  
Figure 9: Axial force distribution curve. (**a**) Anchorage length 10 m; (**b**) Anchorage length 20 m.  
Through comparison, it is observed that under varying rod end tensions, the axial force of the anchor rod with both anchorage lengths exhibits a gradual attenuation along the anchorage depth. However, the patterns of attenuation differ across various stress stages. The reason for the attenuation of the shorter anchor is that the anchorage length of the short anchor is shorter, the tension can be directly diffused into the surrounding rock and soil, and the stress equilibrium state can be reached quickly between the rock and soil and the anchor, which shows that the attenuation degree is relatively small. Secondly, the short anchor involves a small range of rock and soil, and the properties of the anchored rock and soil are relatively uniform, which makes the axial force attenuation more stable. The reason for the attenuation of the long anchor is that the tensile force transmission path of the long anchor is long, and the stress transmission gradually weakens as the depth increases, resulting in uneven attenuation of the axial force in the long-distance transmission, and the attenuation degree is greater and the distribution is uneven. Secondly, the long anchor passes through a large range of rock and soil, and the properties of rock and soil are obviously different, resulting in different interactions between different positions of the anchor and the rock and soil, which makes the attenuation of the axial force in the long anchor complex and uneven. In addition, the deformation of different parts of the long anchor is inconsistent when it is pulled, which makes the deformation of the rock and soil in some areas inconsistent with that of the anchor, affecting the cohesion and friction, which leads to the reduction of the axial force transmission efficiency, and the attenuation is obvious and uneven. The axial force In the bolt with an anchorage length of 10 m is relatively more uniform compared to the bolt with a 20 m anchorage length, and the degree of attenuation is reduced. The axial force in a bolt with an anchorage length of 10 m is relatively uniform compared to that of a 20 m bolt, showing less attenuation. When the tensile force at the end of the rod is 300 kN, the axial forces at each measurement point for the 10 m anchorage length are 278 kN, 75 kN, and 10 kN, respectively.