## 4 Analysis of Calculation Results  
### Settlement Analysis  
Figures 5-8 display the settlement-time calculation curves for the four negative pore water pressure distribution modes along the sand drain, namely, the \"concave\" parabola, \"convex\" parabola, linear distribution, and uniform distribution. The legend represents the depth from the surface. The results demonstrate that the settlement of the soft foundation increased rapidly during the first 30 days and then gradually slowed down, finally reaching a stable state. The surface soil was subject to the most settlements, which decreased with increasing depth. Settlement changes were faster and more significant closer to the surface and slower and less noticeable further away from the surface. On the 56 th day, the surface settlement reached 82.40 cm under the \"concave\" parabolic distribution of pore water pressure, water pressure, 93.95 cm under the \"convex\" parabolic distribution of pore water pressure, 81.69 cm under the linear distribution of pore water pressure, and 109.33 cm under the uniform distribution of pore water pressure. The settlement-time curve at a depth of 22 m was almost horizontal. On the 56 th day, the settlement deformation at a depth of 22 m reached 2.74 cm, 2.83 cm, 2.75 cm, and 3.27 cm for each of the four conditions, respectively, indicating that the vacuum effect was minimal at a depth of 22 m.  
After vacuuming, within 8 h, the vacuum under the membrane reached over 80 kPa. Negative pore water pressure was transmitted vertically from the sand cushion layer under the membrane to the sand drains, causing a change in pore pressure in the sand drains. Then, the negative pore pressure in the sand drains was transmitted to the surrounding soil. Finally, the soil underwent consolidation under the negative pore pressure. The vertical distribution pattern of the pore pressure in the sand drains determined the horizontal transmission strength of the pore pressure in the surrounding soil. From the assumptions of the four types of sand drain pore pressure distribution modes, it could be known that under the \"concave\" parabolic distribution mode, the average pore pressure was the smallest, while under the uniformly distributed model, the average pore pressure was the largest. So, it could be inferred that the consolidation settlement of soil was in descending order:  
Figure 4: Distribution pattern of pore water pressure along the sand well. Figures 9 and 10 depict the settlement-time calculation curves and measured value curves at depths of 0 m and 4 m under the four different pore water pressure distribution modes. The qualitative development trend of the four calculation curves was consistent with the measured values. During the first 5 days, the four calculated curves were highly consistent with the curves of the measured values. However, a large gap between the four calculated curves and the measured values was observed between days 5 and 30. The maximum difference between the calculated settlement value and the measured settlement value under the concave parabolic and linear distributions occurred around the 10 th day, reaching 8.95 cm. The maximum difference between the calculated settlement value and the measured settlement value under the \"convex\" parabolic distribution occurred around the 30 th day, reaching 12.53 cm. The maximum difference between the calculated settlement value and the measured settlement value under uniform distribution also occurred around the 30 th day, reaching 24.87 cm. After 30 days, the calculated settlement curve and the measured settlement curve under the \"concave\" parabolic and linear distributions had a high degree of coincidence, with differences of 0.724-2.4 cm and 0.01-1.65 cm, respectively. However, the difference between the calculated settlement value and the measured settlement value under the \"convex\" parabolic and uniform distributions was consistent with the difference around the 30 th day. Figure 8: Settlement–time curve under uniform distribution.