# Axial Bearing Mechanism of Post-Grouted Piles in Calcareous Sand
## 2 Outline of the Model System
### Pile Driving Test and Grouting Device  
To achieve the static pressure penetration effect of steel pipe piles, a simple homemade device is used to simulate the penetration process of driving piles in the actual projects. Before the pile driving test, the standing time of the model foundation should not be less than 12 h after the reverse pressure load is removed. Static pressure pile driving mainly consists of three steps: the preparation stage, correction stage, and completion stage. (1) In the preparation stage, the single pile of the model is fixed to the preset position, through the threaded rod and the steel plate, to complete preparation before pile driving. (2) In the correction stage, torque is applied to the steel plate to drive the steel pipe pile to penetrate into the foundation soil. To ensure the verticality of the model pile, a time recorder is used to measure the penetration depth every 2 min to control the pile driving speed, and a horizontal ruler is employed to correct the verticality of the model pile. (3) In the completion stage, an identical method to that in the previous steps is employed to gradually apply static pressure to complete the static pressure pile driving test. During the pile driving test, the required speed of the steel pressing plate must be ensured when torque is applied to control the pile pressurized speed and maintain the verticality of the model pile. The subsequent pile driving test shows that the homemade pile pressurized device can effectively simulate the penetration process of model piles in the actual projects by controlling the penetration rate. In addition, the distance between the model pile and the model container boundary in this test is 8.5\(D\), which meets the requirements of boundary conditions 6\(D\)-8\(D\) during pile sinking [20; 21]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sand Type**} & **Density, \(\rho\)** & **Moisture** & **Void** & **Relative** & **Internal Friction** & **Compression** \\  & **(g\(\cdot\)cm\({}^{-3}\))** & **Content, \(\omega\) (\%)** & **Ratio, \(e\)** & **Density, \(d_{a}\)** & **Angle, \(\varphi\) (\({}^{\circ}\))** & **Modulus, \(E_{\text{s1-2}}\)** \\ \hline Calcareous sand & 1.56 & 22.05 & 0.97 & 2.52 & 36.38 & 15.39 \\ \hline Siliceous sand & 1.68 & 19.78 & 0.84 & 2.58 & 32.31 & 25.13 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physicochemical parameters of the sand foundations. To explore the effect of post-grouting on the response of axially loaded piles in calcareous sand, two types of grouting tests were performed in this study, including grouting at the side of the pile and grouting at the pile shaft with Polyvinyl Chloride (PVC) pipes. Grouting at the side of the pile is referred to as annular point grouting, and grouting at the pile shaft with PVC pipe is referred to as ideal-geometry grouting. A detailed schematic diagram of the two grouting methods is shown in Figure 2. In the annular point grouting test, two grouting pipes are symmetrically arranged in the model pile, and the bottom of the grouting pipe is connected through the hole in the inner side of the tubular pile. The distance between the bottom of the grouting pipe and the pile head is 22.5 cm, the diameter of the grouting pipe is 8 mm, and the hole size of the pile shaft is 8 mm and sealed by a pushpin (Figure 2a). The ideal-geometry grouting test is performed by grouting the PVC pipe set on the pile shaft. After pile driving, the PVC pipe is pressed into the pile circumference with the model pile as the center, and the sand sample is excavated (Figure 2b). Various grouting devices have been developed to satisfy the requirements of the post-grouting test.