# Experimental Study on the Effect of Pile-End Soil on the Pile Load Transfer Law
## 3 Analysis of Test Results
### Analysis of Pile Axial Force  
Through the strain gauges set on the pile body, the strain at each section of the pile body under different loads can be obtained, and the axial force of the pile at each section can be calculated. The calculation formula is:  
\[\mathrm{P_{i}}=\mathrm{A_{P}}\cdot\mathrm{E_{P}}\cdot\mathrm{\varepsilon_{i}}. \tag{1}\]  
Here, \(\mathrm{A_{P}}\) represents the cross-sectional area of the pile. \(\mathrm{E_{P}}\) represents the elastic modulus of the pile. \(\mathrm{\varepsilon_{i}}\) is the strain at the pile section i. \(\mathrm{P_{i}}\) represents the value of the axial force at the pile section i.  
The variation curves of the pile axial force magnitude along the depth for the pile-end soilless compressive pile and the conventional compressive pile are shown in Figure 6.  
Under the vertical load, the axial elastic compression of the pile causes the relative displacement of the pile and soil, thereby generating the skin friction, while the vertical load overcomes the skin friction and transmits down the pile body. As shown in Figure 5, the axial force curve of the pile body is roughly linearly distributed. The steepness of different segments reflects the size of the skin friction of the segment; the steeper the curve, the smaller the skin friction, and vice versa, the greater the skin friction. At the initial stage of loading, the slope change of the axial force curve on the upper part of both test piles is relatively obvious, which indicates that the skin friction at the pile body is fully exerted. At the same depth, as the load increases, the slope of the axial force distribution curve gradually decreases until it is stable. This shows that the skin friction develops gradually with the increase of the load and finally tends to be stable. This is mainly because when the load is gradually increased, the compression and displacement of the pile body increase and the skin friction increases with the increase of the relative displacement until it reaches stability.  
Under different loads, the axial force of the two test piles gradually decreases downward with the depth, reflecting the characteristics of the skin friction gradually exerting from top to bottom along the pile body, and the axial force distribution forms are basically similar but also different: For the axial force distribution of the pile-end soilless compressive pile (Figure 6a), the axial force at the pile-end soilless compressive pile is zero during loading, which directly reflects the successful fabrication of the pile-end soilless compressive pile. The loads are balanced by the skin friction provided by the pile-side soil, and the  
Figure 6: Axial force distribution curve of test pile body: (**a**) the pile-end soilless compressive pile and (**b**) the conventional compressive pile.  
curves are uniformly distributed as the load increases. For the axial force distribution of conventional compressive pile (Figure 6b), the load is mostly borne by the skin friction during the initial loading period. With the increase of the load, the resistance of the pile-end is gradually exerted. Under the ultimate load, the slope of the axial force curve of the pile body becomes smaller, and the axial force at the end of the pile is about 42% of the pile top load, exhibiting the characteristics of an end-bearing friction pile.