# Experimental Study on the Effect of Pile-End Soil on the Pile Load Transfer Law
## 3 Analysis of Test Results
### Evolution of the Skin Friction  
The skin friction distribution curve is normalized, and the abscissa is defined as the segment skin friction divided by the maximum skin friction of the test pile at this level of load, which becomes the pile segment skin friction ratio, and the ordinate is defined as the position of the strain gauge divided by the pile length to become the depth ratio. The normalized curve is shown in Figure 8. The pile-end soilless compressive pile are solid lines, and the conventional compressive pile are dashed lines. In order to describe the variation law of the skin friction ratio of the pile segment conveniently, define 0-0.25 L as the upper part of the pile, 0.25 L-0.5 L as the upper-middle part of the pile, 0.5 L-0.75 L as lower-middle part of the pile, and 0.75 L-L as the lower part of the pile; the length of the pile is L. Figure 8 correspond to the distribution changes and comparisons of the pile segment skin friction ratio of the two piles in the linear stage, the local shear stage, and the failure stage. In Figure 8a, in the linear phase, the pile side frictional resistance of both piles increases and then decreases in the direction of the pile body, and the peak value occurs in the middle and upper part of the pile. In the upper area of the two piles, the pile segment skin friction ratio of the pile-end soilless compressive pile decreases from 0.6 to 0.51, while the pile segment skin friction ratio of the conventional compressive pile increases from 0.43 to 0.5. This indicates that the performance of load transfer on the upper part of the pile-end soilless compressive pile is better than that of the conventional compressive pile when the test piles are in the linear stage. In Figure 8b, In the local shear stage, with the increase of load, the distribution trend of skin friction of the two test piles continued to increase first and then decrease, and the location of peak skin friction did not change. In the upper part of the two piles, the lateral friction ratio of the pile section pile segment skin friction ratio of the two test piles increased continuously but more concentrated as the load increased, indicating that the two test piles behaved in a more consistent manner as the load increased and the skin friction provided by the soil around the upper part of the pile increased gradually reaching the limit. In the middle-lower sections of the pile, the pile segment skin friction ratio of the pile-end soilless compressive pile increases from 0.48 to 0.84, while the pile segment skin friction ratio of the conventional compressive pile increases from 0.49 to 0.68. In the lower part of the pile, the pile segment skin friction ratio of the pile-end soilless compressive pile increases from 0.3 to 0.67, while the pile segment skin friction ratio of the conventional compressive pile increases from 0.4 to 0.56. Compared with the conventional compressive pile, the pile segment skin friction ratio of the pile-end soilless compressive pile is more variable. It shows that as the load increases, the friction performance of the soil layer around the lower-middle part and lower part of two piles of the pile-end soilless compressive pile is better than that of the conventional compression pile. That is to say, the skin friction of the lower-middle part and lower part of the pile-end soilless compressive pile is exerted to an increasing degree. A large number of experimental studies have shown that only when the vertical load reaches a certain value does the pile-end resistance gradually come into play, and then the pile-end resistance may have an effect on the skin friction. Therefore, the variation of skin friction under ultimate load is an effective means to study the effect of the presence of the pile-end soil on the pile skin friction. From Figure 8c, when the load is in the failure stage, the skin friction of both piles increases to different degrees.