## 5 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Position**} & \multicolumn{5}{c}{**Soil Depth (m)**} & \multicolumn{2}{c}{**Error Ratio (\%)**} \\ \cline{2-7}  & \multicolumn{2}{c}{**Measured**} & \multicolumn{2}{c}{**Estimated**} & \\ \cline{2-7}  & \multicolumn{2}{c}{**Dynamic**} & \multicolumn{2}{c}{**Reference**} & \multicolumn{2}{c}{**Graphical**} & \multicolumn{2}{c}{**Reference**} & \multicolumn{2}{c}{**Graphical**} \\  & \multicolumn{2}{c}{**Cone Test**} & \multicolumn{2}{c}{**P-Wave Velocity**} & \multicolumn{2}{c}{**Bilinear Method**} & \multicolumn{2}{c}{**P-Wave Velocity**} & \multicolumn{2}{c}{**Bilinear Method**} \\ \hline \multirow{4}{*}{BS} & 1 & 0.2 & 1.7 & 0.2 & 750.0 & 0.0 \\  & 2 & 0.9 & 1.4 & 0.9 & 55.6 & 0.0 \\  & 3 & 1.0 & 3.4 & 1.2 & 240.0 & 20.0 \\  & & & Average & & 348.5 & 6.6 \\ \hline \multirow{4}{*}{MS} & 1 & 1.1 & 2.4 & 1.0 & 118.2 & 9.1 \\  & 2 & 0.8 & 2.6 & 0.9 & 225.0 & 12.5 \\  & 3 & 1.0 & 2.4 & 1.1 & 140.0 & 10.0 \\  & & & Average & & 161.1 & 10.5 \\ \hline \multirow{4}{*}{TS} & 1 & 0.4 & 4.4 & 0.6 & 1000.0 & 50.0 \\  & 2 & 1.9 & 5.2 & 2.2 & 173.7 & 15.8 \\ \cline{1-1}  & 3 & 0.9 & 4.2 & 0.9 & 366.7 & 0.0 \\ \cline{1-1}  & & & Average & & 513.5 & 21.9 \\ \hline \multicolumn{7}{l}{Note: error ratio = (estimated value \(-\) measured value)/measured value; the numbers in Position column indicate the testing locations in Figure 3.} \\ \end{tabular}
\end{table} 
Table 1: _Cont._various soil depths can be estimated by the proposed method. The detailed soil depths based on the suggested graphical bilinear method are summarized in Table 1.  
Figure 8: Estimated soil depth profile based on graphical bilinear method: (**a**) 30 m of BTS; (**b**) 80 m of BTS; (**c**) 100 m of BTS; (**d**) 20 m of BS; (**e**) 30 m of MS; and (**f**) 20 m of TS. Figure 7: Method for selecting soil depth through measured elastic wave velocity. Line “a” denotes the first slope between wave velocity and depth. Lines “b”, “c”, and “d” represent the second, third and fourth slopes, respectively. Point “e” is the intersection point between lines “a” and “b”. Note the figure is the relation between wave velocity and depth of point 1 (or 10 m distance) in the BTS line (Figure 3). The measured DPI values at the selected testing sites are plotted in Figure 9 to determine soil depth based on the impaction study. Soil depth is estimated to the maximum penetrated depth at which the DPI value is nearly zero. Even though the DPI shows variation with depth within a borehole, the final penetrated depth can be easily calculated based on the depth where the value of DPI is close to zero. Figure 9c shows that DPI does not converge close to zero until a depth of 2 m. The maximum possible experiment depth is fixed to 2 m due to the rod length and energy transfer during impaction, thus the soil depth is expected to be greater than 2 m. This deeper expected soil depth can be anticipated because the soil thickness was estimated to be approximately 3.0 m based on the graphical bilinear method shown in Figure 8c for the same position as in Figure 9c. Table 1 summarizes the soil depth calculated by dynamic cone penetration tests. Figure 10 shows the comparison of soil depths predicted by the reference P-wave velocity (0.7 km/s) and the graphical bilinear method with the measured depths using dynamic cone penetration test. Note that the depth based on the results of the dynamic cone penetration test (DPI values) has relatively high reliability because the data is gathered through direct penetration of the probe into soil; therefore, the soil depth measured by DPI can be regarded as the real soil depth. The soil depth predicted based on the reference P-wave velocity shows high variation and high soil depth compared with those based on DPI values. In contrast, the soil depth based on the graphical bilinear method shows small variation and the estimated values are comparable with the measured values by dynamic cone test, reflecting the enhanced reliability of the estimated soil depth by using the suggested method.