# The Influence of Radial Stress on Mechanical Properties of Anchorage Structure
## 2 Experimental Programs
### Samples Preparation
#### 2.3.2 Typical Load-Displacement Curves  
As seen from Figure 6, the typical load-displacement curve of debonding failure goes through four stages: Linear stage (OA), hardening stage (AB), softening stage (BC), and frictional force stage (CD). Figure 7 shows the typical load-displacement curve of splitting failure (sample 2-3). Comparing that with Figure 6, it can be seen that the trend of the two is similar before point B, and the corresponding loads of points A and B are also close. From point B, the interface between the grouting body and concrete begins to appear debonding. The curve of splitting failure does not soften like the curve of debonding failure, but with the increase of displacement, the load continues to increase until the peak point P. At this time, the pullout load of anchorage structure reaches 59 kN, which is more than ten times larger than the ultimate load of 3.5 kN when the interface is debonding in Figure 6.  
Figures 6 and 7 are load-displacement curves of sample 2-0 and sample 2-3 respectively. There is no difference between them except the sand content of grouting materials. However, the failure modes of the two are different and the difference of their ultimate loads is more than expected. After further analysis of the failure mode of the samples, it is found that the majority of the samples with splitting failure are those with more sand content in the cement mortar. The main reason for this phenomenon  
Figure 5: Splitting failure. Figure 6: Typical load-displacement curve of debonding failure (sample 2-0). is that interface debonding begins to appear between the grouting body and concrete and the relative sliding occurs with the increase of the pullout load. At this time, the dilatancy effect will occur at the interface between the grouting body and concrete. As the interface roughness of the grouting body with sand content is higher, the dilatancy effect is more obvious. The interface between the grouting body with high sand content and the concrete produces a larger dilatancy in the radial direction of anchorage section, which directly leads to the increase of normal stress at the interface. The increase of normal stress directly improves the shear strength of the interface, which will greatly improve the ultimate bearing capacity of the anchorage structure. Under these test conditions, there is no radial confining pressure or restraint around the concrete. When the tensile stress caused by the radial stress around the borehole exceeds the tensile strength of the concrete, the concrete is split. It is not difficult to see from the load-displacement curves of the failure samples that when the stress reaches the peak value, the anchorage structure \"suddenly collapses\" due to the splitting failure of the concrete, which completely loses the bearing capacity. Table 4 shows the failure loads of samples with 1:0 and 1:3 cement-sand ratio under the same anchorage length. From the above failure modes and test data, it is not difficult to find out that the higher the sand content in the grouting body under the same conditions, the greater the failure load of the sample. On the face of it, all the differences are affected by the sand content in the grouting body. In fact, the interface roughness of the grouting body with high sand content is high, which makes the radial stress on the interface due to dilatancy increase significantly. It is conceivable that if a certain confining pressure is applied around the sample, the ultimate bearing capacity of the entire anchorage structure will be higher. In conclusion, the existence of radial stress in the anchorage section can significantly improve the bearing capacity of anchorage structure. Similar phenomena have been reported in the experimental studies conducted by other scholars. [PERSON] et al. [27] pointed out that there are compression, dilatancy,