# Analysis of Load-Settlement Curve Based on Load Transfer at Pile-Soil Interface
## 4 Analysis of Pile Settlement Mechanism
### Load-Settlement Fluctuation Law of Test Piles  
As shown in Figure 8a,b, the measured settlement-time curves of test piles S1#, S2#, and S3# are essentially the same as the general \"S-shaped\" curve. The settlement of the pile increased in a linear proportion during the first 605 min of the loading process, and the major consolidation settlement rate of the soil is quicker with 0.197 mm/h for test pile S1#, 0.364 mm/h for test pile S2#, and 0.407 mm/h for test pile S3#. After 605 min, the consolidation rate of the soil steadily reduces and the settlement tendency gradually moderates; during the first 255 min of the unloading process, the settlement grew with the load steadily reducing, and the pile settlement rate gradually tended to lessen with the extension of time, with 0.23 mm/h for test pile S1#, 0.429 mm/h for test pileS2#, and 0.47 mm/h for test pile S3#. The elastic compression deformation and primary consolidation settling dominate settlement at this stage. After 255 min, the settlement pace has become moderate and soft and the settlement has essentially converged. This is due to an incomplete slag at the pile end of test pile S1#, which gradually hardened with pile top loading; The bearing layer of test piles S2# and S3# is primarily a pulverized sandy soil layer with some clay, which takes longer to consolidate and has a more visible settlement tendency. The load-settlement curve of the test pile, as shown in Figure 9a-c, is of the slow-varying type. When the pile top load is modest, the pile top settlement of S1# is minimal and develops slowly, with a settlement of around 30 mm. The pile tip settlement is about 2.5 mm and the pile compression is approximately 27.5 mm. The top load-settlement of piles S2# and S3# grew more rapidly, where the pile top settlement is approximately 66 mm for test pile S3#, the pile end settlement is approximately 15 mm, and the pile compression is approximately 30 mm; while the pile top settlement is approximately 56 mm for pile S2#, the pile end settlement is approximately 12.5 mm, and the pile compression is31 mm. After unloading, the settlement of the pile top grows slowly for test heaps S1#, S2#, and S3#, whereas the settlement of the pile end practically did not create rebound for test pile S1#. Due to less silt at the bottom of the pile, no rebound was created when the pile bottom sediment solidified during unloading. Since pile compression, linear elastic deformation has happened, and hence the settlement change of the pile top is generally steady. Test piles S2# and S3# contain a thick layer of silty caly under the pile end, and the load of the pile end creates rebound and residual deformation during unloading; the final residual volume for test pile S2# is about 10 mm, and the final residual volume for test pile S3# is approximately 11 mm. Figure 8: (**a**) Loading settlement–time curve; (**b**) Unloading settlement–time curve. As shown in Figure 10, the load-pile compression curve is a percentage of the pile top settlement separated into four stages for test piles S1#, S2#, and S3#. The first stage is 0-160 t, which means \"unchanged stage\". At this stage, the pile top load is tiny, the pile end has not yet operated, and the maximum settlement of the pile end is around 0.5 mm, while the pile compression accounts for 99% of the pile top settlement--which practically all of the settlement originates from the pile compression at this time--and the test pile exhibits the characteristics of a pure friction pile. The second stage is 160-240 t, which is known as the \"slow change stage\". At this stage, the pile end begins to move gradually and the settlement rises in tandem with the  
Figure 10: Load-pile compression as a percentage of pile head settlement. Figure 9: (**a**) Pile head load-settlement curve; (**b**) Pile tip load-settlement curve; (**c**) Pile compression load-settlement curve. load. The maximum settlement is around 2.6 mm. The compression accounts for 89% of the pile top settlement and the amount reduces as the pile top settlement falls.