## 2 Torque Transmission Mechanism and Experimental Scheme
### Design and Fabrication of the Experimental Scale Model  
To study the torque transfer mechanism in a foundation ring wind power expanded infrastructure, a 1:3 scale model test on a 1.5-MW onshore wind power infrastructure with a 70-m tower was carried out. Considering the effects of factors (e.g., foundation ring depth, thickness of the bottom flange, and concrete strength) on the bearing capacity of the foundation, the inherent mechanism was analyzed in detail. The size of the original 1.5 MW wind turbine foundation is shown in Figure 3.  
Considering that there is a certain degree of discretion in the performance of the concrete structure, to obtain the system's experimental data while combining the actual onsite conditions, some parameters of the original drawings should be adjusted, e.g., reducing the foundation ring depth, the thickness of the foundation ring flange, and the strength grade of the concrete. According to the same ratio of 1:3, four scale models were fabricated (see Table 1), and their monitoring devices were installed. In this batch of scale model tests, the geometric similarity ratio \(C_{L}=1/3\), material of the same intensity was used, i.e., the elastic modulus similarity ratio \(C_{E}=1\), and the density similarity ratio \(C_{\rho}=\)1. The model similarity theory was strictly followed, and similar criteria for other physical quantities can be obtained using the dimensional analysis method, as listed in Table 2[33; 34; 35]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Specimen No.** & **Specifications** \\ \hline ZT-1 & Original size of standard scale specimen (C35); \\ ZT-2 & With reduced foundation ring depth (C35) \\ ZT-3 & With reduced width and thickness of foundation ring flange (C35) \\ ZT-4 & With reduced strength grade of concrete (C25) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Concrete parameters of bucket foundation. Figure 3: 1.5 MW wind turbine foundation: (**a**) foundation size (mm); (**b**) half-section stereogram of the prototype foundation. When selecting the foundation ring and reinforcement, the primary scale, based on the basic scale, is selected. Then, the plate thickness and diameter that are closest to the calculated values are selected. The prototype size of the foundation ring and steel reinforcement, as well as the calculated scale size and the actual size of the model, are shown in Table 3. Note that the foundation ring plate thickness and steel reinforcement diameter can only be chosen from existing models on the market, while the basic ring components and opening sizes can be laser cut and processed to meet the requirements for model size in practice. Four scale models were fabricated, as shown in Figure 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Physical Property** & **Physical Parameter** & **Similar Relation** & **Remark** \\ \hline \multirow{6}{*}{Geometric relation} & Length & \(C_{L}\) = 1/3 & Control size \\  & Line displacement & 1/3 & - \\  & Area & \(C_{A}\) = 1/9 & - \\  & Volume & \(C_{V}\) = 1/27 & \\  & Density & \(C_{\rho}=1\) & \\  & Angular displacement & 1 & - \\  & Strain & \(C_{\rm s}=1\) & - \\ \hline \multirow{6}{*}{Material relation} & Strength & 1 & \\  & Elastic modulus & \(C_{\rm E}\) = 1 & Control material \\  & Stress & \(C_{\rm\sigma}\) = 1 & - \\  & Density & 1 & - \\  & Quality & \(C_{\rm Q}=C_{V}\)-\(C_{\rm\rho}\) =1/27 & - \\ \hline \multirow{6}{*}{Load relation} & Gravity acceleration & 1 & \\  & Concentrated load & \(C_{P}=C_{L}^{2}\)-\(C_{E}=1/9\) & Control experiment \\  & Line load & 1/3 & - \\  & Surface load & 1 & - \\  & Moment & \(C_{M}=C_{L}^{3}\)-\(C_{E}=1/27\) & - \\  & Shear & 1/9 & - \\ \hline Reinforcement on & Longitudinal reinforcement \(A_{\rm s}\) & 1/9 & - \\ cross-section & Longitudinal reinforcement \(A_{\rm sv}\) & 1/9 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Similar relationships between the experimental scale model and the original prototype.