# Advanced Scanning Technology for Volume Change Measurement of Residual Soil
## 7 Discussion  
The soil classified as MH (inorganic silt and fine sand) exhibits notable characteristics, such as a high plasticity index of 28%, a moderate void ratio of 0.42, and a saturated coefficient of permeability of 2.65 \(\times\) 10\({}^{-6}\) m/s, indicating low to moderate drainage capabilities [58]. The grain size distribution, consisting of 42% sand, 30% silt, and 28% clay, suggests a balanced texture that influences its mechanical behavior and water retention properties [59]. High plasticity can lead to challenges like shrink-swell behavior, which is critical in engineering applications, particularly for foundation design and earthworks, where moisture fluctuations can affect stability and performance [60].  
The shrinkage curve from 3D scan measurement indicates a change in void ratio from the initial condition of 0.68 to 0.48 at the end of the tests. The decrease in void ratio is considered moderate from saturated water content of 24% to 15%. This change is associated with moderate reduction in pore spaces and water content, leading to densification which automatically results in a higher density at the end of shrinkage test.  
Figure 10 and Table 3 show the differences in the air-entry values and inflection points between macro and micro pores suggest significant changes in water retention characteristics as soil suction increases. This behavior cannot be shown in Figure 11 and Table 4. Incorporating a shrinkage curve appears crucial for accurately modeling the SWCC, as indicated by the discrepancies observed in the model without it. The incorporation of a shrinkage curve into the SWCC significantly influences the accuracy of water retention modeling in soils. When soil experiences changes in moisture content, it can undergo volumetric shrinkage, particularly in fine-textured soils. This shrinkage alters the soil structure, affecting pore size distribution and connectivity. By integrating the shrinkage curve, the model better accounts for the gradual transition of moisture levels and the associated changes in pore sizes. This ensures that the air-entry values and inflection points reflect more realistic conditions, particularly in how macro and micro pores behave under varying suctions. Without this consideration, models may inaccurately predict saturation levels, leading to erroneous conclusions about soil behavior in real-world applications.  
Moreover, the presence of a shrinkage curve provides insight into the mechanical properties of the soil as it dries and shrinks. For instance, as suction increases, the effective stress within the soil matrix changes, which can impact not only water retention but also soil strength and stability. This is particularly critical in engineering applications, where understanding the interplay between moisture content, pore pressure, and soil structure can inform decisions related to construction, land management, and agricultural practices. Thus, including a shrinkage curve in the SWCC modeling enhances its predictive capabilities and offers a more comprehensive understanding of soil behavior under fluctuating moisture conditions.