## 3 Results and Discussion
### Earth Pressure Analysis of the Composite Structure  
Figure 8 shows the earth pressure on the cantilevered sections of the existing and new piles under different working conditions. For working condition 1, the earth pressure of the existing pile increased and decreased with the distance from the top of the existing pile. The maximum earth pressure was 3.019 kPa at about one third from the ground line. The earth pressure was lower than the passive earth pressure and higher than the static earth pressure at each position. Field measurements have shown a similar trend for the earth pressure [20]. The main reason is that the soil behind the wall undergoes stress during mechanical rolling or vibration, resulting in earth pressure increases. Under working condition 2, the earth pressure of the existing pile became higher as the upper backfill load increased. The earth pressure decreased as the distance from the top of the existing pile increased. It was equal to the static earth pressure at the top and the active earth pressure at the bottom. However, the earth pressure of the new pile increased with the distance from the top. The earth pressure from the new pile top to the existing pile top was slightly higher than the static earth pressure. In contrast, the earth pressure decreased from the top of the existing pile to the ground line and was lower than that of the existing pile. The maximum earth pressure occurred near the top of the existing pile (1.797 kPa). Under working condition 3, the earth pressure of the existing pile increased with the distance from the top of the pile under a uniform load. It affected the lower part of the cantilever, and the maximum earth pressure was 7.367 kPa. In contrast, the earth pressure from the top of the new pile to the top of the existing pile was small. The new piles had full contact with the existing sheets from the top of the pile to the ground. Since the new piles and the existing piles have similar lateral bearing capacities, the maximum earth pressure occurs at the same position on the new and existing piles. The maximum earth pressure was 6.540 kPa. The earth pressure was higher in working conditions 4 and 5 than in the other working conditions at all locations on the existing pile. The earth pressure of the new pile increased and decreased as the distance from the new pile top to the existing pile top and from the existing pile top to the ground increased, respectively. The main reason is a sudden change in the composite stiffness of the pile and the soil at the top of the existing pile and the ground. The upper composite stiffness is lower than the lower composite stiffness [21; 22]. In working conditions 4 and 5, cracks appeared in the new sheet in the middle and propagated upward (Figure 9a). Figure 9b shows that the vertical and lateral deformation are larger under a uniform upper load. The main reasons are that the soil near the pile cannot be thoroughly compacted due to the narrow space, and the viscoplastic deformation is large due to step excavation  
and backfilling. Thus, the retaining structure is adjacent to the void, and the stiffness is low. Transverse deformation and shear cracks caused by the upper load occurred, which is consistent with field-measured data [20,23]. Figure 10 shows the additional earth pressure under the strip load. At an upper load amplitude of q, the additional earth pressure of the pile top was slightly different for the new and existing piles. A large difference in the earth pressure was observed between the top of the existing pile and the ground line, and the rate of increase was higher for the new than for the existing pile. At an upper load amplitude of 2q, the rate of increase in the additional earth pressure was similar for the new and existing piles. The new pile had a larger rate of increase than the existing pile at the ground.