# Advanced Scanning Technology for Volume Change Measurement of Residual Soil
## 6 Results  
The specific gravity, grain-size distribution, Atterberg limits, and soil classification are shown in Table 2. It can be seen that the soil consists predominantly of fines, exhibits high plasticity, and can be classified as MH soil under the Unified Soil Classification System (USCS). Figure 8 depicts the w-SWCC data for the Tampines soil specimen. The \(w\)-SWCC discrete data are fitted using Equation (2) since it shows unimodal shape. The measurement data of soil and water volume change with time using the proposed 3D scan method are converted into void ratio against gravimetric water content, called shrinkage curve. Figure 9 shows the average data of shrinkage curve from 10 sets of 3D scans. The SWCC data, in terms of degree of saturation against suction (\(S_{r}\)-SWCC), are established using the shrinkage curve from 3D scanning measurements. Figure 10 depicts the \(S_{r}\)-SWCC for Tampines specimen with shrinkage curve from 3D scan measurement. The discrete data of the SWCC in Figure 10 are best fitted using Equation (3) since it shows a bimodal shape. Figure 11 shows the \(S_{r}\)-SWCC for the Tampines specimen after ignoring the shrinkage curve from the 3D scan data. The discrete data of SWCC in Figure 11 are best fitted using Equation (2) since it shows a unimodal curve. To prevent excessively large \(m\), \(n\), and \(\theta_{s}\) values, these parameters are limited to a maximum of 6. Tables 3 and 4 show the parameters used for best fitting. \begin{table}
\begin{tabular}{c c} \hline
**Properties** & **Value** \\ \hline Bulk density, \(\rho\) (Mg/m\({}^{3}\)) & 2.15 \\ Water content, \(w\) (\%) & 16.3 \\ Void ratio, \(e\) & 0.42 \\ Liquid limit, LL (\%) & 52 \\ Plastic limit, PL (\%) & 24 \\ Plasticity index, PI (\%) & 28 \\ Specific gravity, \(G_{s}\) & 2.65 \\ Grain size distribution—gravel (\%) & 6 \\ Grain size distribution—sand (\%) & 52 \\ Grain size distribution—silt (\%) & 20 \\ Grain size distribution—clay (\%) & 22 \\ Unified Soil Classification System (USCS) & MH \\ Saturated coefficient of permeability, \(k_{s}\) (m/s) & \(2.65\times 10^{-6}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Index properties. Figure 8: SWCC of soil specimen from Tampines with respect to gravimetric water content. Figure 10: SWCC of Tampines soil specimens with regard to degree of saturation, using shrinkage curve from 3D scan. Figure 9: Shrinkage curve of soil specimen from Tampines. Table 3 indicates the fitting parameters for the shrinkage-incorporating SWCC as shown in Figure 10. Table 3 shows distinct differences between the macro pore (sub-curve 1) and micro pore (sub-curve 2). The air starts to enter soil macro pores when suction is around 320 kPa (air-entry value of sub-curve 1, \(\psi_{a1}\)). The pore size that has maximum number of pores can be found within suction around 1500 kPa (suction at inflection point of sub-curve 1, \(\psi_{m1}\)). The air starts to enter soil micro pores when suction is around 125,000 kPa (air-entry value of sub-curve 2, \(\psi_{a2}\)). The pore size that has maximum number of pores can be found within suction around 200,000 kPa (suction at inflection point of sub-curve 2, \(\psi_{m2}\)). Table 4 shows the best-fitting parameters of the SWCC which does not include the shrinkage curve as presented in Figure 11. The fitting parameter of \(a\) = 600 does not represent the air-entry value of 600 kPa. Figure 11 indicates the decrease in degree of saturation happens from beginning of test which is not reasonable. The fitting parameters \(n\) and \(m\) are associated with the shape of SWCC which has steep slope of SWCC. Figures 10 and 11 indicate the importance of accurate measurements of soil volume change. As the soil suction increased up to 100 kPa, volume changes were observed from \begin{table}
\begin{tabular}{c c} \hline
**Properties** & **Value** \\ \hline \(a\) & 600 \\ \(n\) & 1.6 \\ \(m\) & 0.5 \\ \(C_{r}\) & 1500 \\ Residual suction, \(\psi_{r}\) (kPa) & 20,000 \\ \hline \end{tabular}
\end{table}