## 3 Results and Discussion
### The Influence of Soil Response on Cumulative Deformation of the Pile Group
The cause is that the P2 and P3 sensors were situated in the middle of the foundation soil, where the pore water in the soil surrounding the pile is unable to dissipate rapidly under the influence of horizontal cyclic loading, resulting in an escalation of pore water pressure. However, the pore water pressure in the location of the P1 sensor tended to decrease in the later period. This is likely because the water in the pore space was continuously discharged from the crack with the development of the crack in the later period, and the pore water pressure was gradually dissipated with the increase of the crack. In order to investigate the trend of pore water pressure development in relation to the varying pile spacings, this study employed pile 2 as a representative case for analysis. Figure 12 depicts the development of pore water pressure for pile spacings set at 3, 4, and 5 times the pile diameter, with a depth of 2 times the pile diameter (the location of the P4 sensor). The results revealed the same variation pattern for the pore water pressure at different pile spacings: It underwent rapid development during the initial 1000 cycles,  
Figure 11: The variations in pore water pressure. (**a**) The location of the P1 sensor (a depth of 2 times the pile diameter). (**b**) The location of the P2 sensor (a depth of 8 times the pile diameter). (**c**) The location of the P3 sensor (a depth of 14 times the pile diameter). followed by a subsequent declining trend. However, significant differences in values were observed beyond 1000 cycles. Specifically, the pore water pressure under pile spacing set at 3 times the pile diameter demonstrated an increase of approximately 30% compared to that of pile spacing set at 4 times the pile diameter. Similarly, the pore water pressure under pile spacing set at 4 times the pile diameter showed an increase of about 25% compared to that of pile spacing set at 5 times the pile diameter. This observation indicates that the cumulative effect of pore water pressure weakens with a larger pile spacing due to the pile group effect. Additionally, a shorter pile spacing results in a higher pore water pressure, as the softening of saturated clay becomes more prominent due to the decrease in effective stress within the soil, leading to larger horizontal cumulative deformation of the pile group. In addition, from Figures 11 and 12, it can be found that the super pore water pressure on the pile side was basically consistent with the trend of cumulative deformation of the pile group. Therefore, the cumulative deformation process of the pile group can be explained by the generation of super pore water pressure and the dissipation of super pore water pressure in the process of cyclic loading. During the development stage of horizontal deformation of the pile group, the excess water in the pore space of the soil on the pile side may not be able to effectively drain in the early stage, resulting in rapid accumulation of excess pore water pressure under the influence of horizontal cyclic loading. According to the effective stress principle, the effective stress decreases with the rise of  
Figure 12: The variations in pore water pressure. (**a**) File spacing is set at 3 times the pile diameter. (**b**) File spacing is set at 4 times the pile diameter. (**c**) File spacing is set at 5 times the pile diameter. pore water pressure, which directly leads to the decrease of soil strength, the increase of soil deformation, and the sharp increase of horizontal deformation of the pile group. In the later stage, due to the accumulation rate of super pore water pressure on the pile side gradually decreasing, the growth rate of soil deformation decreased, and the accumulation rate of horizontal displacement of the pile group became slow. In the stabilization stage of pile group horizontal deformation, the super pore water pressure on the pile side no longer increased, the soil deformation tended to be smooth, and the pile group horizontal accumulated deformation tended to be stable.