## 5 Result and Interpretation
### Classification of the Weathering Grade  
The relative weathering coefficient of the stone materials for each face were calculated based on the ultrasonic velocity of the fresh pink feldspar granite and leucogranite at the provenance site of the stone block foundation of the Sungryemun Gate (Figure 7). The weathering of the new and original blocks in both the south and north faces is clearly different. Overall, the south face, which has more new blocks than the north face, exhibits diverse weathering characteristics, from the fresh stage to the completely weathered stage.  
A quantitative comparison was conducted between the relative and absolute coefficients of the stone block foundation of the Sungryemun Gate by combining the weathering coefficients, K, of each point of the ultrasonic measurement by each block. The relative weathering grade of the original blocks based on the ultrasonic velocity of the fresh rock at the provenance site exhibits a normal distribution that is centered on the moderately weathered stage (63.6%); however, the stages are observed to be mainly from the fresh (55.2%) to the slightly weathered stage (41.4%) for the new block (Figure 8a, Table 7).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Elevation** & \multicolumn{2}{c}{**Rock Type**} & **Mean** & **Min.** & **Max.** & **SD** \\ \hline \multirow{4}{*}{South} & \multirow{2}{*}{Original block} & Pink feldspar granite & 2859 & 1235 & 4644 & 717 \\  & & Leucogranite & 2571 & 1402 & 3704 & 492 \\  & & Total & 2783 & 1235 & 4644 & 677 \\ \cline{2-6}  & \multirow{2}{*}{New block} & Pink feldspar granite & 3892 & 2360 & 4732 & 473 \\ \hline \multirow{4}{*}{North} & \multirow{2}{*}{Original block} & Pink feldspar granite & 2601 & 1431 & 4360 & 441 \\  & & Leucogranite & 2577 & 1351 & 4471 & 401 \\  & & Total & 2591 & 1351 & 4471 & 426 \\ \cline{2-6}  & \multirow{2}{*}{New block} & Pink feldspar granite & 3869 & 2564 & 4762 & 520 \\ \hline \multirow{4}{*}{Overallelevation} & \multirow{2}{*}{Original block} & Pink feldspar granite & 2713 & 1235 & 4644 & 591 \\  & & Leucogranite & 2575 & 1351 & 4471 & 430 \\ \cline{1-1}  & & Total & 2665 & 1235 & 4644 & 545 \\ \cline{1-1} \cline{2-6}  & \multirow{2}{*}{New block} & Pink feldspar granite & 3884 & 2360 & 4762 & 488 \\ \hline \end{tabular}
\end{table}
Table 6: The mean, minimum, and maximum ultrasonic velocities (m/s) and standard deviations of the original and new blocks.  
Figure 6: Contour maps of the ultrasonic velocities of the stone block foundation.  
Figure 8: Histograms and pie diagrams of weathering classification in original and new blocks. (**a**) Relative weathering degree. (**b**) Absolute weathering degree.  
Figure 7: Block maps of weathering coefficient, K, in case of the stone block foundation. (**a**) Relative weathering grade. (**b**) Absolute weathering grade.  
Furthermore, from the absolute weathering grade based on the ultrasonic velocity (5000 m/s) of a universal hard rock, majority of the original blocks were observed to be at the highly weathered stage (72.3%), while approximately 7.1% of the blocks were at the completely weathered stage. However, the new blocks were almost evenly split between the moderately (54.0%) and slightly (42.5%) weathered stages (Figure 8b, Table 7). To summarize, the original and new blocks of the stone block foundation of the Sungryemun Gate differed by approximately two weathering stages. The absolute weathering grade tends to underestimate the overall physical properties and strength of the blocks compared with the relative weathering grade.