## 2 Test Overview
### Test Scheme  
The static load test of the single pile was carried out using the pile load method, in which the ballast platform counterforce device was used for loading, and the counterforce was provided by the counterforce frame. One hydraulic jack with a rated output of 630 tons was used to apply pressure, and the loading load was measured by a hydraulic gauge parallel to the jack. The top pile settlement was automatically measured by four displacement transducers installed symmetrically. The field test is shown in Figure 3.  
Figure 1: Arrangement of reinforcement in two PHC piles.  
Figure 2: Inner digging method construction process.  
To study the load-bearing characteristics of pipe pile foundations constructed by the medium boring method and to further study the pile-soil interaction and pipe pile load transfer law. Both test piles were equipped with a rebar gauge. The arrangement of the rebar meter is shown in Figure 4. In order to ensure the normal operation of the rebar meter, four rebar meters were arranged symmetrically in each section when the rebar was installed. Each section had eight rebar meters; 24 for one pile and 48 for two test piles.  
In this project, the static load test of the foundation pile adopted a slow maintenance load method; the upper pile load was a concrete block placed on the longitudinal beam, and the lower part of the longitudinal beam was in contact with the main reaction beam while the reaction loading device was placed on the pile at one end and in contact with the main reaction beam at the other end. The grading of loading and unloading, as well as the reading of top pile settlement, was by JGJ106-2014 after each level of load was applied, the top pile settlement was read at 5, 15, 30, 45, and 60 min, and then every 30 min. When unloading, each load level was maintained for 1 h, and the next load level could be unloaded after the settlement of the pile top was measured and read at 15, 30, and 60 min. After unloading to zero, the residual settlement at the top of the pile was measured and read; the maintenance time should not be less than 3 h, the reading time is the fifteenth and the thirtieth min, and then readings were taken every 30 min. The loading series and the initial and maximum loads on two test piles were given in Table 2.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Layer Number**} & \multirow{2}{*}{**Soil Type**} & \multirow{2}{*}{\begin{tabular}{c} **Soil** \\ **Thickness** \\ **(m)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Cohesion** \\ **(kPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Internal** \\ **Friction** \\ **Angle** \\ **(c’)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Compression** \\ **Modulus** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Shear** \\ **Modulus** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Stiffness** \\ **(N/m)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Density** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} } \\ \hline
1 & Silty clay & 1.5 & 14.7 & 21.7 & 5.349 & 3.101 & \(2.35\times 10^{13}\) & 1900 \\
2 & Silt & 1.7 & 12.0 & 24.5 & 7.472 & 5.984 & \(3.86\times 10^{13}\) & 2040 \\
3 & Fine Sand & 12 & 0 & 18.0 & 19.556 & 6.175 & \(8.05\times 10^{13}\) & 2030 \\
4 & Silt & 2.1 & 25.0 & 25.0 & 24.510 & 9.398 & \(6.95\times 10^{13}\) & 2030 \\
5 & Clay & 2.3 & 14.7 & 21.7 & 5.3 & 3.1 & \(7.2\times 10^{13}\) & 2000 \\
6 & Silty Clay & 10.5 & 12.5 & 25.0 & 5.8 & 3.5 & \(2.65\times 10^{13}\) & 2010 \\
7 & Clay & 1.9 & 0 & 18 & 20.6 & 6.2 & \(1.95\times 10^{13}\) & 2000 \\
8 & Fully Weather & & & & & & & \\ Sandstone & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Geophysical and mechanical parameters of the soil layer.  
Figure 3: Static load test.