## 4 Test Results and Discussion
### The Test Results for Part One  
The research emphasis of this part is about the influence of outer diameters of helix on recycling torque of single-plate helical pile. The test results about the recycling torque (\(T_{\text{R}}\)) of a single-plate helical pile; the embedment depth (\(z\)) responses of single-plate helical piles; the vertical force on the central shaft (\(F_{\text{push}}\)) of a single-plate helical pile; and the embedment depth (\(z\)) responses of single-plate helical piles with same size of the pitch of helix, \(p\) = 0.03 m, different outer diameters of helixes, \(D_{\text{H-out}}\) = 0.12 m, 0.16 m, and 0.20 m, and same recycling speed, \(v_{\text{R}}\) = 1 \(p\)/\(r\), are compared in Figures 6-8. According to the results of Figures 6-8, we made the following observations:  
1. The changing trends of the recycling torque, \(T_{\text{R}}\), of the single-plate helical piles in dense sand with different outer diameters of the helix are the same and all consist of three parts: For the first part, the recycling torque, \(T_{\text{R}}\), increases sharply from the beginning of recycling process until the recycling torque reaches a peak value. For the second part, the recycling torque decreases with a relatively slow speed after the peak value. After the process of the second part, the recycling torque decreases sharply when the helix is close to the ground's surface.
2. Besides, the recycling torque, \(T_{\text{R}}\), of the single-plate helical piles increases with the rise of the size of the out diameter of helix, \(D_{\text{H-out}}\).
3. For the vertical force on central shaft, \(F_{\text{push}}\), of the single-plate helical piles, it also has that similarly changing trend of the recycling torque, \(T_{\text{R}}\)--that of the single-plate helical piles. It increases sharply from the beginning of the recycling process, and after that it drops stably from the peak value until the helix is close to the soil's surface. Similarly, the vertical force on central shaft, \(F_{\text{push}}\), of the single-plate helical piles, also increases with the raise of the size of the out diameter of helix, \(D_{\text{H-out}}\).
4. According to the change trends of the vertical force on central shaft, \(F_{\text{push}}\), and the recycling torque, \(T_{\text{R}}\), of the single-plate helical piles, their vibration changes are synchronous, which means \(F_{\text{push}}\) also has an effect on \(T_{\text{R}}\).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**The Test Identifier** & \(D_{\text{H-out}}\) **(m)** & \(v_{\text{R}}\) **(\(p\)/\(r\))** & \(p\) **(m)** & **Test Number** \\ \hline \(R\)-OD-0.12-\(1p\) & 0.12 & 1 & 0.03 & TN-1 \\ \(R\)-OD-0.16-\(1p\) & 0.16 & 1 & 0.03 & TN-2 \\ \(R\)-OD-0.20-\(1p\) & 0.20 & 0.8 & 0.03 & TN-3 \\ \(R\)-OD-0.20-\(0.8p\) & 0.20 & 1 & 0.03 & TN-4 \\ \(R\)-OD-0.16-\(p\)-0.06-\(0.5p\) & 0.16 & 0.5 & 0.06 & TN-5 \\ \(R\)-OD-0.16-\(p\)-0.1-\(0.5p\) & 0.16 & 0.5 & 0.10 & TN-6 \\ \(R\)-OD-0.16-\(p\)-0.16-\(0.5p\) & 0.16 & 0.5 & 0.16 & TN-7 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Experimental program and key results.  
Figure 6: The test results of test number one (TN-1). (**a**) Recycling torque. (**b**) Vertical force on shaft.  
Figure 7: The test results about TN-2. (**a**) Recycling torque. (**b**) Vertical force on shaft.