## 2 Field Testing on Uplift Capacity in Composite-Anchor Cable Uplift Pile
### Results of Load Tests on Site  
Figure 1 illustrates the displacement curve of the pile top under uplifting loads for the three sets of test piles. In this depiction, the variable \(U\) signifies the pile-top load, while \(\delta\) represents the pile-top uplifting displacement. The load-displacement curve of the Type-A test pile displays a steep profile, while those of the Type-B and Type-C test piles exhibit gentler characteristics. During the initial loading phase, the Type-A pile's top displacement increases nearly linearly with the growing uplifting load. However, as the uplifting load surpasses 6160 kN, the uplifting displacement experiences a sudden change, marking a distinct turning point. As per the Technical Code for the Testing of Building  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Pile** & **Length** & **Diameter** & **Pile Material** & **Hole-Forming** & **Estimated Uplift** \\
**Number** & **(m)** & **(mm)** & & **Method** & **Bearing** \\  & & & & & **Capacity (kN)** \\ \hline Type-A & 22 & 800 & C35 & Mud rotary drilling & 4400 \\ Type-B & 22 & 800 & C35 & Mud rotary drilling & 4400 \\ Type-C & 22 & 800 & C35 & Dry rotary drilling & 4400 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Information on the three types of test piles [20].  
Foundation Piles (JGJ 106-2019) [23], this turning point designates the onset of a significant increase in the single pile's ultimate carrying capacity for the Type-A pile. In contrast, the vertical displacement of the pile tops for the Type-B and Type-C piles exhibits consistent and gradual increases at each loading level, devoid of abrupt variations. According to the specifications, the determination of the ultimate bearing capacity for each test pile should be based on the load value at the preceding level where the \(\delta\)-lgt curve's slope exhibits a notable increase or the curve's tail displays a significant bend. Therefore, the ultimate load results of the static load test for each pile are shown in Table 2. It is important to note that the alteration in the measurement method for displacement only impacts the displacement data of the composite-anchor piles. Consequently, the displacement data for Type-A remains unchanged from previous articles, while the displacement data for Type-B and Type-C are derived from this experiment.  
An in-depth analysis of the U-\(\delta\) curves shows similar initial uplift displacements among the different pile types. However, as the applied load increases, the displacement of the new piles (Type-B and Type-C) gradually exceeds that of the conventional pile (Type-A). Comparing the Type-A and Type-B piles, the uplift bearing capacity of the Type-A piles is approximately 16.7% higher. It is important to note that both Type-A and Type-B piles surpass the estimated bearing capacity of 4400 kN, meeting the design requirements for the uplift bearing capacity. On the other hand, comparing the Type-B and Type-C piles reveals that Type-C piles have an approximately 18.2% higher bearing capacity than Type-B piles. This significant difference can be attributed to the use of the dry rotary drilling method for hole formation in Type-C piles, which prevents the formation of a mud skin between the pile body and the surrounding foundation soil, thereby improving stress conditions and reducing deformation. Furthermore, the uplift bearing capacity of Type-C piles increases by approximately 1.3% compared to Type-A piles.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Ultimate Load of Vertical** & **The Uplift Amount** \\
**Pile Number** & **Uplift Bearing Capacity Test** & **Corresponding to the Test** \\  & **(kN)** & **Ultimate Load (mm)** \\ \hline Type-A & 6160 & 21.40 \\ Type-B & 5280 & 14.01 \\ Type-C & 6240 & 17.63 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Results of static load test on single pile.  
Figure 1: Load–displacement curve of three test piles.