## 2 Experimental Study
### Model Setup  
The soil chosen for the study is the typical Wuhan sand, with composition percentages of 70% sand, 25% silt, and 5% clay. The soil was meticulously layered and compacted  
Figure 1: Diaphragm wall foundations with different sections and combinations. in a sealed test pit measuring 200 cm \(\times\) 200 cm \(\times\) 160 cm, enclosed by sealing panels. Rigorous control was exercised over the compaction density of each soil layer to guarantee the desired strength and deformation characteristics of the soil. This meticulous approach aimed to achieve uniformity across the entire soil mass. During the filling process, the compaction density of each soil layer was measured using the ring knife method, while the moisture content of the soil was determined using the oven-drying method. To ensure the quality and uniformity of the filling process, static cone penetration tests (CPT) were conducted on the soil before and after saturation [26]. The test results indicated good overall uniformity of the soil, with an average density of 1.78 g/cm\({}^{3}\). The experimental model of the GPF utilized in this study was constructed from organic glass with a consistent thickness of 40 mm. The pile cap employed a steel adjustable pile diameter assembly model for the footing, as illustrated in Figure 2. During the experiment, the GPF was fixed to the footing using bolts, while the pile cap had high strength and could be considered rigid for this experiment [27]. As shown in Figure 3, the soil was layered and filled within a steel test pit with a dimension of 200 cm \(\times\) 200 cm \(\times\) 160 cm. The test pit was partitioned into four evenly sized zones, where the soil was meticulously layered and compressed to guarantee a consistent distribution across each zone. The total height of the soil box is 150 cm, with the GPF embedded at a depth of 80 cm. After installing the GPF, the pile cap is securely connected to the GPF using slots and bolts, ensuring a stable foundation connection. The loading system used in the experiment employs the MTS Large-Scale Servo Static Loading System, located in the Structural Building of China University of Geosciences (Wuhan). The loading system consists of a 25-ton actuator, reaction steel beam, hydraulic  
Figure 3: Experimental layout. Figure 2: Proposed hydrostatic test model: **(a)** GPF, **(b)** pile cap. pump, and MTS specialized control software. To monitor the variation of lateral stress in the soil, a certain number of soil pressure cells are installed within the soil. These cells are designed to measure real-time lateral stress parameters during the experiment. The displacement sensor in the MTS loading system's actuator enables real-time monitoring of the displacement at the top of the pile throughout the entire loading process. These data are recorded for subsequent analysis. For the measurement of lateral stress in the soil, DYMH-106 miniature soil pressure cells are used. Before the experiment, these pressure cells are calibrated and then placed and compacted in each soil layer to ensure good compaction and prevent any issues with poor compaction [28]. The depths at which the soil pressure cells are installed are 20 cm, 40 cm, 70 cm, 90 cm, and 110 cm. The soil pressure cells inside the pile are placed at the center position of the pile foundation, while the cells outside the pile are placed at lateral distances of 5 cm, 17 cm, and 39 cm from the pile body. Additionally, to consider the edge effect, one soil pressure cell is placed at a distance of 5 cm from the side of the model box, at a depth consistent with the distribution of the soil pressure cells near the pile foundation. The experimental setup involves lateral static loading, where the GPF is subjected to both vertical and lateral loads. The arrangement of the MTS actuator and data acquisition system is shown in Figure 4. A vertical actuator applies a constant vertical force of 5 kN at the top of the GPF to simulate the axial loading of the superstructure on the pile foundation.