## 3 Experimental Setup and Procedure
### Test Procedure  
To minimize the error caused by the disturbance of loading and maintain the loading stress level, a lever loading system was designed, comprising the bearing plate under the pivot (angle steel), a one-end hinged lever (universal beam), and balance weight blocks (Figure 9) [43]. The surcharge load was imposed on the soil through the bearing plate with a length and width of 300 mm and 200 mm, respectively, and the net horizontal distance between the bearing plate and the model piles was 40 mm.  
The surcharge loading was applied by manually adding several balancing weights of the same mass, 60 kg, on the lever system. To be specific, the initial uniformly distributed load caused by the self-weight of the lever loading system (comprising the pressure bearing plate, angle steel, universal beam, and loading basket) is \(p_{0}=9.375\) kPa; the increments of  
Figure 8: Installation of dial indicators: (**a**) locations of the dial indicators; (**b**) rigid PVC pipes; (**c**) schematic for the lateral displacement measurement of the model pile.  
Figure 9: Lever loading system: (**a**) hinged end; (**b**) bearing plate under the pivot; (**c**) balance weight blocks in the loading baskets.  
\(p_{1}=25\) kPa between different loading levels can be applied by adding a balance weight of 60 kg into the loading basket. Therefore, the total uniform distributed surcharge is \(p=p_{0}+p_{1}\times(n-1)\), where \(n\) represents the loading stages. To sum up, the surcharge of each stage is \(p=9.375\), 34.375, 59.375, 84.375, 109.375, 134.375, 159.375, and 184.375 kPa. Therefore, in this study, six groups of tests were tested under eight loads (five groups of free tip piles with pile inclinations \(\beta=-20^{\circ}\), \(-10^{\circ}\), \(0^{\circ}\), \(+10^{\circ}\), and \(+20^{\circ}\), and one group of the fixed tip pile with a pile inclination \(\beta=-20^{\circ}\)).  
The vertical stress caused by the self-weight of the actual embankment is 179 kPa, and the idealized embankment surcharge in the model test should be designed to be slightly greater than the equivalent vertical stress caused by self-weight to include all the loading cases. However, due to the change in the physical and mechanical parameters of the pile-soil system in the scaled test (especially the reduction of pile size), the scaled surcharge that corresponds to a 10 m high embankment should be less than 179 kPa. The maximum vertical stress under the loading plate is 184.375 kPa, about 103% of the actual surcharge, which is applied by the lever system with seven balance weight blocks with a mass of 60 kg.  
The data were noted before and after loading and collected every 30 min. The loading at every stage sustained at least 1 h, and the loading at the adjacent stage was initiated after the displacement was steady (the discrepancy between the last two notes of the dial indicators was less than 0.1 mm). The pile deflections can be directly measured by dial indicators, and the bending moments \(M\) can be derived from the data measured from the strain gauges, \(M=E_{\mathrm{P}}I_{\mathrm{P}}\cdot(\epsilon_{\mathrm{t}}-\epsilon_{\mathrm{c }})/b\), \(\epsilon_{\mathrm{t}}\) and \(\epsilon_{\mathrm{c}}\) are the tension strain and compression strain, respectively. The region division of earth pressure and subgrade reaction is related to the depth of the rotation center, and the depth can be determined by the zero point of the earth pressure on the left side. The earth pressures can be directly obtained according to the data collected by the earth pressure cells at the left side of the pile above the rotation center. The subgrade reactions were estimated by the data collected by the earth pressure cells at the right side of the pile above the rotation center and the left side of the pile beneath the rotation center.