# Improved Mandel System for Prefabricated Vertical Drain Installation: A Macro to Micro Analysis
## 4 Results and Discussion
### Microstructure Analysis
#### 4.2.2 Soil Structure  
1. Soil structure before vacuum preloading  
Kaolinite is a clay mineral that can form a soft soil with high water content. In Figure 16, an SEM image of the soil before the consolidation test is shown, and the corresponding size distribution is described in Table 6. The SEM image of kaolinite specimens with different fabrics is consistent with the conclusion obtained from the sedimentation test [43; 44]. In addition, the samples varied in several factors, such as the sample preparation method, imaging conditions, and the nature of the material [45]. Figure 16: SEM image of kaolinite before the test. Figure 15: The three types of PVD including pore and particle analyses: **(a)** all PVD types in terms of size; **(b)** all PVD types in terms of percentage. In this study, SEM images showed a relatively smooth and uniform surface at lower magnifications, with some voids and visible pores. The edges of the particles appeared slightly rounded or irregular due to the presence of water. At higher magnifications, the SEM image revealed the platy structure of the kaolinite particles, which were stacked or arranged in a random orientation. The particles were tightly packed together, with little space between them, or more loosely packed, with visible voids and gaps. In some areas, the SEM image showed small aggregates of particles, indicating the presence of localized bonding between the particles. The aggregates were irregular in shape, and the surfaces showed some textural variation, including cracks, fissures, or other features. Overall, the structure of kaolinite soft soil with high water content appeared relatively homogeneous and uniform, with some variability in the particle arrangement and texture visible under higher magnification. The SEM image provides valuable information about the microstructure and properties of the soil, which can help to inform engineering and construction decisions. 2. Soil structure after vacuum preloading SEM images were used to study the changes in soil structure due to vacuum preloading. SEM can provide high-resolution images of soil particles and their arrangements, allowing us to observe the changes in the soil microstructure due to consolidation [46; 47; 48]. Taking into consideration the PVD, pore, and particle results, the bottom area of the PVD was determined as a clogging area. Further analysis was necessary to understand the effect of PVD in the three areas. Figure 17 shows the SEM images from the three areas, highlighting the effect of PVD after vacuum preloading on the soil structure. The SEM images show that the soil particles became more closely packed after vacuum preloading. The soil particles became more tightly interlocked, resulting in a denser soil structure with face-to-face contact between particles and domains [49]. Furthermore, the morphology of soil particles was affected by vacuum preloading [50; 51]. For example, clay particles became more angular or irregularly shaped, indicating that vacuum preloading altered the soil particle properties. To explain these results more clearly, an analytical approach was carried out in this study, and the results are shown in Figure 18. It can be seen that the pore and particle areas for PVD type B were 0.5 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\) and 0.7 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\) in the inner smear zone, 0.3 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\) and 1.1 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\) in the transition zone, and 0.7 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\) and 0.7 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\) in the undisturbed zone. The corresponding values for type A were 1.2 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\) and 2.4 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\), 0.9 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\) and 2.7 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\), and 0.8 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\) and 2.7 \(\times\) 10\({}^{3}\)\(\upmu\)m\({}^{2}\), respectively.