# Analysis of Load-Settlement Curve Based on Load Transfer at Pile-Soil Interface
## 4 Analysis of Pile Settlement Mechanism
### Analysis of Internal Forces at the Pile-Soil Interface
#### 4.3.2 Force Analysis of Pile-Soil Interface Friction Resistance  
The connection between axial force and lateral friction resistance is stated in Equation (6). The lateral friction resistance of each layer of soil is considered to be the same during the calculation procedure, and \(\tau_{\text{arg}i}\) is the average of the lateral frictional resistance in stratiform soil, which may be represented as follows [19]:  
\[\tau_{\text{arg}i}=\frac{P_{i}-P_{i-1}}{A_{i}} \tag{6}\]  
In which, \(P_{i}\) and \(P_{i+1}\) are the axial forces of the \(i\)-th and \(i\)+1-th sections, and \(A_{i}\) is the lateral area of the \(i\)-th layered pile. Figure 12 depicts the distribution curves of the lateral frictional resistance along test piles S1#, S2#, and S3# under various load levels. For test piles S1#, S2#, and S3#, as illustrated in Figure 12a-c, the lateral frictional resistance is non-linearly distributed over the pile body and progressively increases with increasing pile top load. The lateral frictional resistance is greater in the higher and lower parts of the pile, whereas it is reduced at a depth of 15 m. The presence of a thick layer of silt soil on the lateral of a pile reduces the lateral frictional resistance, which is owed to lower rebound and loosening in silt soil, and soil tension is discharged with less degradation on the lateral of a pile. The highest value comes at 20 m of embedded depth, which is related to the softening phenomena of lateral frictional resistance and the minor rise in radial earth pressure in the silt clay layer; hence, the lateral frictional resistance reduces by varying degrees as load increases, and then progressively declines and sustains at a certain value. Figure 13 depicts the connection between lateral frictional resistance and pile top load for test piles S1#, S2#, and S3#. Figure 11 shows that the lateral frictional resistance as a  
Figure 12: (**a**) Lateral frictional resistance under different loads for test pile S1#; (**b**) Lateral frictional resistance under different loads for test pile S2#; (**c**) Lateral frictional resistance under different loads for test pile S3#. percentage of pile top load is around 100 percent for test piles S1#, S2#, and S3# at a low load (less than 160 t). The load is borne solely by the lateral frictional resistance at this point, and the test pile acts as a pure friction pile. With increasing pile top load, the pile end resistance tends to \"slowly shift\", the lateral frictional resistance ratio progressively declines, and the pile end plays the function of \"primary force\", at which point the test pile exhibits end-bearing friction pile transition characteristics. When the pile top load achieves the intended load of 220 t, the ratio of lateral frictional resistance to the pile top load (i.e., the lateral frictional resistance ratio) for test piles S1#, S2#, and S3# is 91%, 93%, and 90%, respectively. The lateral frictional ratios of test piles S1#, S#, and S3# at maximum loads of 640 t are 75%, 75%, and 76%, respectively. It can be observed that the pile lateral frictional resistance at maximum load provides the majority of the test pile bearing capacity, while the pile end bearing capacity is only partially given, and the test pile plays the end-bearing friction pile characteristic at this stage. As shown in Table 3, the lateral frictional resistance in clay, silty clay, peitic silty sand, and silt with clay over 15 m of the test pile has varying degrees of weakening, i.e., the measured value to the geological report ratio is less than one. The lateral frictional resistance in silt with clay, clay, and silty sand below 15 m of the pile has a mild strengthening effect, i.e., the measured value to the geological report ratio is more than 1. The lateral dynamic resistance of the soil layer in the lower portion of the pile is not fully developed, with a ratio of only 0.772 between the measured and supplied values of the lateral dynamic resistance of the soil layer towards the pile end.