## 2 Materials and Methods
### Experimental Methods  
#### 2.3.1 Vertical Compressive Static Load Test of Single Pile  
The vertical compressive static load test of a single pile is recognized as the most intuitive and reliable traditional method to detect the vertical compressive bearing capacity of the foundation pile. 1. Preparation before vertical compressive static load test of single pile:  
* Soil treatment around the pile  
A working plane (12 m \(\times\) 12 m), as shown in Figure 3, should be reserved around the test single pile. If the bearing capacity of foundation soil on site is lower, it is usually required by the replacement treatment. * Construction of ballast platform  
The ballast platform is composed of a concrete counterweight block, secondary beam, main beam, lifting jack, etc. The pressure weight of the pile head shall not be less than 1.2 times the estimated maximum test load, and the pressure weight shall be added once before the test and shall be evenly and firmly placed on the platform. When sufficient ballast before the test may cause damage to the foundation soil under the buttress, a small part of the ballast can be added during the test, and it shall be ensured that the ballast is not less than 1.2 times the test load. Figure 4a shows the schematic diagram of the surcharge test device. It is estimated that about 1250 tons of counterweight is required for the ballast platform in this test. The counterweight, steel beam, and other equipment required to build the platform are as follows: 2 steel main beams (0.5 m \(\times\) 1.2 m \(\times\) 10 m), 5 steel secondary beams (0.5 m \(\times\) 0.6 m \(\times\) 8 m), 410 concrete counterweight blocks (0.8 m \(\times\) 1.0 m \(\times\) 1.5 m/3 t), 2 lifting jacks, datum beam, and datum pile (as shown in Figure 4b). Figure 2: “Pile–Column Integration”: (**a**) schematic diagram of composite embedded pile method (unit: mm) and (**b**) construction process. Sensor installation and system detection. The static load test adopts the form that the lifting jack is connected with the oil pump, and the load is applied by the lifting jack, as shown in Figure 4a. The oil pressure can be measured by the pressure sensor parallel to the lifting jack oil circuit, and the load is converted according to the lifting jack calibration curve. In order to ensure the measurement accuracy of the static load test, the accuracy grade of the pressure sensor shall be better than or equal to grade 0.5. When two or more lifting jacks are used for loading, to avoid eccentric loading of the tested pile, the lifting jack type should be the same and work synchronously in parallel. The pressure of the pressure sensor, oil pump, and oil pipe for test under maximum loading shall not exceed 80% of the specified working pressure. In addition, the pile diameter of the test pile is 1300 mm. According to the specification requirements, four displacement sensors are symmetrically arranged in two directions. Figure 4: _Cont_. Figure 3: Schematic diagram of static load test site of the test pile. (Unit: mm). After the installation of all test equipment, a system inspection should be carried out. The detailed detection procedure is to preload the test pile with a small load (about 5% of the maximum test load) to eliminate the non-pile settlement caused by the gap between the whole measurement system and the tested pile itself due to installation, pile head treatment, and other factors. The air from the lifting jack and pipeline needs to be removed, the displacement sensors are preheated. Then there must be a check of whether the pipeline joints and valves leak oil. If everything is normal, unload to zero, and start the formal test loading after the reading displayed by the displacement sensor is stable. 2. Test loading method and displacement observation  
* Test loading method  
The slow maintenance load method is adopted for the test, which is also called progressive loading, and the graded load of the test is 1/10 of the maximum load or the estimated ultimate bearing capacity.