## 5 Result and Interpretation  
### Ultrasonic Measurement Conditions  
The equipment used for the ultrasonic measurement of the stone block foundation of the Sungnyemun Gate was a Pundit-plus instrument by CNS Farnell (Borehamwood, UK), which is extensively used in Republic of Korea and various other countries in rock en \begin{table}
\begin{tabular}{c c c} \hline \hline
**Rock Types** & **Location** & **Velocity (m/s)** \\ \hline \multirow{8}{*}{Granite} & Geochang in Korea [44] & 3946 \\  & Geochang in Korea [44] & 3877 \\  & Geochang in Korea [44] & 3680 \\  & Iksan in Korea [44] & 3360 \\  & Yangju in Korea [44] & 4062 \\  & Gimcheon in Korea [44] & 4980 \\  & Geumsan in Korea [50] & 5200 \\  & Jecheon in Korea [50] & 3901 \\  & Jecheon in Korea [51] & 3650 \\  & Ganghwa in Korea [51] & 4600 \\  & Yeosu in Korea [51] & 3470 \\  & Hwangdeung in Korea [51] & 3230 \\  & Malanjkhand in India [52] & 5983 \\  & Mean & 4149 \\ \hline \multirow{2}{*}{Graniodiorite} & Gimcheon in Korea [50] & 4500 \\ \cline{2-3}  & Monzonite & - & 5000 \\ \hline \multirow{4}{*}{Diorite} & Gongju in Korea [44] & 4594 \\  & Gongju in Korea [44] & 4724 \\  & Chungju in Korea [44] & 3826 \\  & Mean & 4381 \\ \hline \multirow{2}{*}{Gabbro} & Macheon in Korea [51] & 3370 \\ \cline{2-3}  & Basalt & Delhi in India [51] & 5760 \\ \hline \multirow{2}{*}{Granite gneiss} & Gimcheon in Korea [50] & 4290 \\ \cline{2-3}  & Gneiss & Massiac in France [53] & 5000 \\ \hline \multirow{2}{*}{Quartzite} & Nagpur in India [50] & 5800 \\ \cline{2-3}  & Wanju in Korea [44] & 4866 \\  & Jeongseon in Korea [51] & 4620 \\ \cline{2-3}  & Isparta in Turkey [54] & 4309 \\ \cline{2-3}  & Mean & 4598 \\ \hline \multirow{2}{*}{Limestone} & Isparta in Turkey [54] & 6355 \\ \cline{2-3}  & Travertine & Isparta in Turkey [54] & 4309 \\ \hline \multirow{2}{*}{Sandstone} & Boyeong in Korea [44] & 5101 \\ \cline{2-3}  & Sangju in Korea [51] & 3770 \\ \cline{1-1}  & Mean & 4436 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The P-wave velocities of fresh rocks. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Weathering Coefficient \(K\)**} & \multicolumn{2}{c}{**Relative Weathering Grade**} & \multicolumn{2}{c}{**Absolute Weathering Grade**} \\ \cline{2-3}  & **Pink Feldspar Granite** & **Leucogranite** & \\ \hline I & FR \(\leq\) 0 & \(\geq\)3829 & \(\geq\)4036 & \(\geq\)5000 \\ II & 0 \(<\) SW \(\leq\) 0.2 & 3063 \(\leq\) SW \(<\) 3829 & 3229 \(\leq\) SW \(<\) 4036 & 4000 \(\leq\) SW \(<\) 5000 \\ III & 0.2 \(<\) MW \(\leq\) 0.4 & 2297 \(\leq\) MW \(<\) 3063 & 2422 \(\leq\) MW \(<\) 3229 & 3000 \(\leq\) MW \(<\) 4000 \\ IV & 0.4 \(<\) HW \(\leq\) 0.6 & 1532 \(\leq\) MW \(<\) 2297 & 1614 \(\leq\) MW \(<\) 2422 & 2000 \(\leq\) MW \(<\) 3000 \\ V & 0.6 \(<\) CW \(\leq\) 1.0 & \(<\)1532 & \(<\)1614 & \(<\)2000 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The P-wave velocity (m/s) ranges of relative and absolute grades of the stone block foundation based on the weathering coefficient, \(K\)[32]. gineering and for a stone architectural heritage. The ultrasonic pulse voltage was set to 1200 V. The stone block foundation of the Sungmyemun Gate has surface irregularities that impact transducer and decrease the repeatability and reliability of measurements. There, the exponential transducer (a nominal 54-kHz frequency) with a 6-mm contact area and dried rubber clay couplant, which does not leave a residue, was used for the measurements. This setup is suitable for performing ultrasonic measurements of rough surfaces, such as that of a stone architectural heritage [25, 55]. Water increases the ultrasonic velocity when it fills pores and microcracks of rocks [56]. Accordingly, the on-site ultrasonic measurements were considered drying conditions of the stone block foundation that are unaffected by the rain. The path length between the transmitter and receiver was set to 200 mm using the indirect method.