## 3 Analysis of Test Results
### The Time-Dependent Behavior of the Uplift Pile Bearing Capacity  
The ultimate uplift bearing capacity of the model pile was obtained through static loading tests on the pile foundation. The increase in bearing capacity after resting for 60 days compared to 1 day is shown in Table 4.  
From Table 4, it can be observed that:  
The ultimate pullout bearing capacity of the model piles increases with the increase in resting time. Among the piles, piles 7\({}^{\#}\), 4\({}^{\#}\), 1\({}^{\#}\), and 3\({}^{\#}\) exhibit significant increases, all exceeding 300%, with the maximum increase reaching 350%. In contrast, piles 9\({}^{\#}\), 5\({}^{\#}\), and 2\({}^{\#}\) have relatively smaller increases of 180%, 188%, and 195%, respectively. The ultimate pullout bearing capacity of a single pile exhibits a rapid increase in the initial phase of testing, followed by a more gradual rise in subsequent stages. This behavior can be ascribed to the pronounced structural and thixotropic characteristics of the Zhanjiang Group structured clay. During soil sampling and preparation, the natural soil structure is compromised, leading to reduced soil strength and consequently a lower pullout capacity for the model piles. As the resting period is extended, the soil structure begins to rehabilitate, enhancing the thixotropic effects. The cohesion and internal friction angle of the soil surrounding the piles gradually return to higher levels. Since the ultimate pullout capacity primarily depends on the cohesion and frictional forces between the pile and the surrounding soil, it exhibits notable time-dependent characteristics. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Pile Number**} & \multicolumn{2}{c}{**Pullout Ultimate Bearing Capacity of Piles After Different Resting Times/N**} & \multirow{2}{*}{**Magnitude of Growth\%**} \\ \cline{2-2} \cline{5-8}  & **1 d** & **7 d** & **14 d** & **28 d** & **60 d** & **90 d** & **Growth\%** \\ \hline
1\({}^{\#}\) & 100 & 220 & 240 & 380 & 430 & 450 & 330 \\
2\({}^{\#}\) & 210 & 330 & 430 & 500 & 620 & 660 & 195 \\
3\({}^{\#}\) & 200 & 360 & 540 & 640 & 830 & 840 & 315 \\
4\({}^{\#}\) & 120 & 270 & 300 & 400 & 520 & 530 & 333 \\
5\({}^{\#}\) & 260 & 350 & 530 & 640 & 750 & 800 & 188 \\
6\({}^{\#}\) & 250 & 430 & 670 & 810 & 900 & 950 & 260 \\
7\({}^{\#}\) & 180 & 340 & 540 & 750 & 810 & 920 & 350 \\
8\({}^{\#}\) & 320 & 580 & 770 & 1150 & 1200 & 1250 & 275 \\
9\({}^{\#}\) & 500 & 720 & 850 & 1230 & 1400 & 1450 & 180 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Ultimate uplift bearing capacity of pile after different rest times. Figure 2: Logarithmic relationship between cohesion, internal friction angle, and standing time. Figure 3 shows a comparative diagram of the effects of pile length and diameter on the load-displacement curves of the pullout piles for model piles 1\({}^{\sharp}\), 5\({}^{\sharp}\), and 8\({}^{\sharp}\) at different resting times. From Figure 3, it can be inferred that:  
1. The U-s curves for each single pile exhibit a sharp decline and have distinct inflection points. When the pile length and diameter are the same, as the resting time increases, the pullout load and the top displacement of the model piles in the ultimate pullout state both increase. This can be attributed to the restoration of the surrounding soil strength with increasing resting time, which enhances the cooperative working ability of the pile-soil system. Consequently, the model piles have a greater pullout strength reserve, leading to improved pullout capacity and increased top displacement. 2. A comparative analysis of 5\(\mu\) (L = 900 mm, D = 25 mm) and 8\({}^{\sharp}\) (L = 900 mm, D = 40 mm) was conducted on the displacement corresponding to the failure load at different rest periods. It was found that when the pile length is 900 mm, as the pile diameter increases from 25 mm to 40 mm, the displacement at the pile head corresponding to the ultimate state of the model pile becomes smaller.