# Pull-Out Test and Mechanical Properties Analysis Based on Intelligent Bolt and Internet of Things
## 4 Test Result Analysis
### Analysis of Ultimate Uplift Bearing Capacity  
Based on the results of the pull-out test, the tensile load and displacement of the rod end are summarized in Table 2, which is used to determine the ultimate pull-out bearing capacity. Based on the criteria for determining the ultimate uplift bearing capacity of the anchor rod, the data in Table 2 show that the displacement increments at the rod end for anchor rods with anchorage lengths of 10 m, 12 m, and 16 m are 300 kN, 320 kN, and 340 kN, respectively. These increments are 2.8 times, 2.7 times, and 3.1 times greater than those produced by the previous load. Therefore, the ultimate uplift bearing capacity is 260 kN, 300 kN and 320 kN. The displacement increments of the last-stage loading of the anchor rod with the anchorage lengths of 20 m and 30 m are 2.0 times and 2.2 times that of the displacement increment of the previous stage loading, and the rod end tension-rod end displacement curve has a steep drop section at 380 kN. Therefore, the upper rod end tension of 340 kN and 360 kN is taken as its ultimate uplift bearing capacity. The curve representing anchorage length vs. ultimate pull-out bearing capacity is presented in Figure 8.  
From the diagram, it can be seen that with the increase in anchorage length, the ultimate uplift bearing capacity increases, but the two do not increase linearly, and the growth ratio is different. The anchorage length increases from 10 m to 12 m and 16 m; the length increases by 20% and 33%, respectively; the ultimate bearing capacity increases by 15.4% and 26.9%, respectively, and the growth ratio is about 0.8. The anchorage length is increased to 20 m and 30 m, respectively; the length is increased by 100% and 200%; the ultimate bearing capacity is increased by 23.1% and 38.5%; and the growth ratio is about 0.2. By comparison, it is found that the growth ratio is the same when the anchorage lengths are 12 m and 16 m, and the ultimate bearing capacity is obviously improved by 0.8. When  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Anchorage Length** & **Load/KN** & **Displacement/mm** & **Load/KN** & **Displacement/mm** & **Load/KN** & **Displacement/mm** \\ \hline
10 m & 220 & 6.1 & 260 & 7.5 & 300 & 11.5 \\
12 m & 260 & 7.4 & 300 & 11.2 & 320 & 21.5 \\
16 m & 280 & 8.6 & 320 & 12.3 & 340 & 23.7 \\
20 m & 300 & 10.0 & 340 & 15.1 & 380 & 25.3 \\
30 m & 340 & 11.0 & 360 & 16.1 the anchorage length reaches 20 m, the growth ratio is only 0.2, and the ultimate bearing capacity increases little with the increase in length. When the anchorage length increases from 20 m to 30 m, the ultimate bearing capacity only increases by 11.8%. Therefore, by increasing the length of the bolt, the improvement of the ultimate pull-out bearing capacity is limited. The anchorage length of the long bolt in the loess layer selected in this test is recommended to be 10-16 m.  
According to the above test results, the anchorage length has a non-linear relationship with the ultimate pull-out bearing capacity. The reason is that, compared with the short anchorage length, the tension diffusion attenuation of the long anchorage length is large, the stress of the distal rock and soil mass is small, and the contribution of the new length to the bearing capacity is reduced. With the increase in anchorage length, the bolts pass through different regions; the bearing contribution of some regions is limited, and the stress transfer is uneven, which makes the bearing capacity growth nonlinear. The growth rate of pull-out capacity decreases with the increase in anchor length. The analysis shows that with the increase in anchorage length, the relative displacement between bolt and rock mass is more likely to be unevenly distributed. In the process of long bolt drawing, the loading end first shows a large relative displacement, which leads to the failure of interface bonding force, the occurrence of interface slip, and the decrease in friction force and bonding force.