## 3 Test Results
### Horizontal Strain  
The horizontal strain of slurry can reflect the degree of uneven consolidation, making it a useful parameter for evaluating the clogging of slurry. Moreover, existing studies on vacuum preloading tests based on PIV technology predominantly use horizontal strain as an indicator to assess slurry clogging [35; 46]. Therefore, in this study, horizontal strain was selected as the key parameter for evaluating the clogging of slurry.  
The cloud diagrams of the horizontal strain in the flocculated slurry are presented in Figure 11. Following the initiation of the vacuum preloading test, a zone with a horizontal strain greater than zero developed near the PVD, indicating that the slurry in this region had begun to consolidate, leading to the formation of a clogging zone [35]. A higher horizontal strain value within the clogging zone corresponds to greater compression and a higher degree of clogging in the slurry. Considering that the clogging zone varies with depth, this study utilized the average width along the depth to characterize the evolution of the clogging zone over time.  
At the completion of the vacuum preloading test, the widths of the clogging zones for the lime-flocculated slurry, the APAM-flocculated slurry, the dual use PAC and APAM-flocculated slurry, and the untreated slurry were 165 mm, 46 mm, 71 mm, and 41 mm, respectively. The average horizontal strain values near the PVD for these slurries were approximately 20%, 35%, 30%, and 40%, respectively. Notably, the horizontal strain value of the slurry gradually decreased along the radial direction from the PVD, indicating a progressive reduction in the degree of clogging with increasing distance from the PVD.  
Figure 11: Horizontal strain fields of slurry. (**a**) Untreated slurry, 3 h; (**b**) untreated slurry, 24 h; (**c**) untreated slurry, 96 h; (**d**) untreated slurry, 168 h; (**e**) lime-flocculated slurry, 3 h; (**f**) lime-flocculated slurry, 24 h; (**g**) lime-flocculated slurry, 96 h; (**h**) lime-flocculated slurry, 168 h; (i) APAM-flocculated slurry, 3 h; (j) APAM-flocculated slurry, 24 h; (**k**) APAM-flocculated slurry, 96 h; (I) APAM-flocculated slurry, 168 h; (**m**) dual use of PAC and APAM-flocculated slurry, 3 h; (**n**) dual use of PAC and APAM-flocculated slurry, 96 h; (**p**) dual use of PAC and APAM-flocculated slurry, 96 and PAC and APAM-flocculated slurry, 168 h.  
Among the tested slurries, the untreated slurry exhibited the smallest clogging zone width and the highest degree of clogging. The boundary of the clogging zone in the untreated slurry displayed extremely dense horizontal strain gradient lines (Figure 11d), indicating a severe non-uniform consolidation phenomenon. This phenomenon can be attributed to the early-stage development of a high-strain clogging zone near the PVD (Figure 11b) in the untreated slurry, which hindered the further transmission of vacuum pressure and significantly reduced consolidation efficiency.  
In contrast, after flocculation treatment, the horizontal strain in the slurry was significantly reduced, and the width of the clogging zone increased considerably. This indicates that flocculation treatment effectively mitigated slurry clogging and facilitated the transmission of vacuum pressure over a greater distance. Among the flocculated slurries, the APAM-flocculated slurry exhibited only a 5 mm increase in the clogging zone width compared to the untreated slurry (Figure 11i), and its horizontal strain values remained relatively close to those of the untreated slurry, suggesting a weaker effect in mitigating clogging. The dual-use PAC and APAM treatment showed a moderate improvement over APAM alone in reducing clogging. The lime-flocculated slurry demonstrated the largest increase in clogging zone width among all treatments (Figure 11h) and exhibited an extremely low horizontal strain, indicating that lime treatment had the most pronounced effect in mitigating clogging caused by vacuum preloading.