# Model Tests on Jacked Pile Penetration Characteristics Considering a Static Press-in Piling Machine
## 3 Test Results and Analysis
### Pile Shaft Unit Side Friction Resistance  
The variation curve of the unit side friction resistance of the pile shaft with respect to the pile penetration depth is depicted in Figure 10. It is evident from the figure that the overall trend of change in the unit side friction resistance of the pile shaft is similar in both test groups. As the pile depth increases, the unit side friction resistance of the pile shaft also increases.  
The analysis of PS1 and PS2 in Figure 10 leads to the conclusion that in the case of test PS2 taking the static press-in piling machine into consideration, the maximum value of unit side friction resistance is 5.44 kPa in PS2, which is obviously larger than that of the 4.46 kPa observed in PS1. It can be attributed to the impact of the pile machine. The soil surrounding the pile experiences lateral squeezing forces, resulting in soil compaction. Therefore, this leads to an increase in the unit side friction resistance of the pile shaft.  
The data from the two test groups in Figure 10 illustrate that, at a soil depth of 10 cm, the unit side friction resistance of the pile shaft gradually decreases with an increase in pile depth at the same soil depth, exhibiting a certain regularity. For every 10 cm increase in penetration depth, the reduction value of the unit side friction resistance becomes more significant. This phenomenon, known as \"side resistance degradation\", has been confirmed by [PERSON] and [PERSON] [30] in experiments. Upon the results, it is concluded that as the pile jacking depth increases, the same soil depth experiences repeated ploughing action, leading to the destruction of the adhesion point between the pile and the soil. Simultaneously, the repeated ploughing increases the thickness of the slurry water film between the pile and the soil, ultimately causing a decrease in pile side friction.  
Then analyze the trend of the \"side resistance degradation\" phenomenon as the soil depth varies in Figure 10a,b. Upon normalization of the difference (\(\Delta f\)) between the \"side resistance degradation\" values \(\Delta f_{\text{PS1}}\) obtained from pile test PS1 and \(\Delta f_{\text{PS2}}\) obtained from pile test PS2, as illustrated in Figure 11, it is evident that all difference values surpass 0. This indicates that the \"side resistance degradation\" in test PS1 is more prominent than in test PS2. In other words, the \"side resistance degradation\" of the unit side friction in test PS2 is generally weakened compared to in test PS1. Furthermore, it can be inferred that as the pile jacking depth increases, \(\Delta f\) gradually decreases. The largest differences in the side resistance degradation occur at depths of 20 cm and 30 cm, signifying that test PS2 exhibits the most significant weakening of \"side resistance degradation\" at these depths.  
Figure 10: The curve of unit side friction resistance of pile shaft with the depth of pile jacking. (**a**) Test PS1. (**b**) Test PS2.  
The analysis of the findings in Figure 11 suggests that the lateral squeezing pressure exerted by the static press-in piling machine on the soil enhances the tightness of the adhesion point between the pile and the soil, thereby increasing the contact firmness between the pile and the soil. As a result, this generally reduces the occurrence of \"lateral resistance degradation\". Despite the influence of the piling machine, the plough force between pile and soil remains strong as the depth of the pile sinking increases, which results in a reduction in the adhesion point between the upper soil and the pile, as well as a decrease in \(\Delta f\). This indicates a gradual reduction in the weakening effect of the piling machine on \"side resistance degradation\". Analysis of the pile sinking resistance reveals significant lateral extrusion at depths of 20 to 30 cm and the maximum \(\Delta f\) at 20 cm and 30 cm caused by the piling machine in this test, which also means the attenuation value of \"side resistance degradation\" is the highest at these soil depths.