## 3 Analysis of Test Results
### Study on Traits of Lateral Frictional Resistance of the Test Piles  
The ultimate side resistance is the rock-soil resistance generated on the side surface of the pile body when the pile top bears the ultimate load. By monitoring and recording the pile axial force distribution, the calculation of the pile lateral frictional resistance can be carried out. The force state of the pile section is shown in Figure 7.  
The lateral frictional resistance of the pile unit is calculated as follows:  
\[\pi dL_{i}f_{i}=N_{i+1}-N_{i} \tag{1}\]  
where \(d\) and \(L_{i}\) are the diameters of test piles and length of pile section, respectively, \(f_{i}\) is pile side frictional resistance per pile section, \(N_{i+1}\) is the top axial force for each pile section, and \(N_{i}\) is the end axial force for each pile section.  
Figure 8 shows the distribution of the lateral frictional resistance of the pile body at all levels of loading. It can be seen from Figure 8 that under working load, the upper part of the pile body is first subjected to elastic compression, generating a lateral resistance of the soil upwards against the pile body. As the load is transmitted down the pile body, the lateral resistance of the pile body is gradually applied from the top downwards and is distributed non-linearly along the pile body. During the loading process the unit lateral  
Figure 6: Axial force distribution along the pile body of PHC\(-\)1 and PHC\(-\)2 under different loads, (**a**) PHC\(-\)1; (**b**) PHC\(-\)2.  
Figure 7: Diagram of load transfer from soil layers.  
resistance distribution of each test pile increased along the depth of the pile body, which is because at the beginning of the loading the lateral resistance of the pile is small, and the load-carrying capacity is mainly provided by the lateral frictional resistance of the upper soil layer. With an increase in the load on the top of the pile, the soil pressure on the part of the pile located in the deep soil layer is much greater than that on the part of the pile located in the shallow soil layer, resulting in a greater increase in the lateral resistance of the deep soil layer. The lateral resistance of the shallow soil layer increases more than the lateral resistance of the shallow soil layer. The lateral resistance generated by the geotechnical layers gradually increases and accounts for the major part of the bearing capacity. Under an ultimate load, the lateral resistance provided by the geotechnical soil reaches its ultimate state, after which the end resistance becomes the main part of the load-carrying capacity, showing the characteristics of an end-loaded pile. In the 0-13 m soil layer, the lateral resistance of test pile PHC\(-\)1 showed a parabolic shape along the length of the pile. In the early stage of loading, the lateral resistance of the pile in the silt layer did not increase significantly, and with an increase in load, the lateral resistance of the pile changed more and more obviously with depth. In soils of 15-25 m, the lateral resistance curve of the pile appears to inflect at around 18 m, when the lateral resistance of the pile first increases and then decreases along the pile body. In the 15-25 m soils, the pile lateral resistance curve inflects at around 18 m, when the pile lateral resistance first increases and then decreases. In contrast, the pile lateral resistance of PHC\(-\)2 increased along the length of the pile throughout the loading process, with no decreasing inflection point in the curve, indicating that the inner digging method can increase the lateral resistance of the pile compared to the conventional construction process. This conclusion is consistent with previous research (i.e., [PERSON] HL et al. 2019). This again confirms that the pile lateral resistance is susceptible to the pile depth.