## 5 Conclusions  
The shear strength parameters of grades IV and V granite, whose friction angles are hard to evaluate with SPT-N values, were evaluated using chemical weathering indices. The shear strength parameters were measured by interpreting the results of PMTs performed at the three test sites in which the grade IV and V granite were deeply developed. The four chemical weathering indices (i.e., VR, CIA, I\({}_{\text{mob}}\), and MWPI) were estimated by XRF, and the relationship predicting the friction angles of grades IV and V granite were suggested based on the weathering indices. The conclusions of this study are as follows:  
1. By interpreting the results of PMTs, the evaluated friction angles of grade IV and V granite in the test sites are estimated from 33.6\({}^{\circ}\) to 52.1\({}^{\circ}\), which is acceptable to the previous studies. However, the friction angles in the particular range decreased with depth, which was different from the general tendency. The weathering profile with depth was studied based on the chemical weathering indices, and the friction angles of grade IV and V granite were evaluated by considering the weathering effect and site-specific characteristics.
2. The weight percentage of alkaline oxides showed a distinct decrease with weathering intensity; however, the alkali oxides did not show a consistent decreasing tendency with weathering intensity. Especially, the composition of K\({}_{2}\)O was reduced because of the decomposition of K-feldspar with weathering, but the leached K ions are used to generate illite.
3. The composition of alkali and alkaline oxides used in the four chemical weathering indices (VR, CIA, I\({}_{\text{mob}}\), MWPI) was consistently decreased with the change in weathering grade at each test site, so the VR, CIA, I\({}_{\text{mob}}\), and MWPI has a typical tendency with weathering and can represent the weathering state of grade IV and V granite.
4. Correlation analysis, including the effect of weathering and site-specific characteristics, was performed to determine the relationship between the chemical weathering indices and friction. The VR, CIA, and I\({}_{\text{mob}}\) have a moderate correlation (R\({}^{2}\) > 0.5). Considering the natural variation of the geotechnical properties, the coefficient of determination is acceptable. The highlight of the present study is the simple method  
Figure 9: Comparison of friction angle with previously suggested correlation using the standard penetration test (SPT)-N value.  
to estimate the friction angle of weathered granite for preliminary site investigation, which is more reliable than the SPT.  
Conceptualization, S.-I.W. and S.-H.L.; Methodology, C.-K.C. and Y.-W.S.; Validation, C.-K.C.; Formal Analysis, S.-H.L.; Investigation, S.-H.L. and Y.-W.S.; Writing-original draft, S.-H.L. and Y.-W.S.; Writing-review & editing, Y.-W.S.; Funding acquisition, C.-K.C.; Project administration, Y.-W.S. All authors have read and agreed to the published version of the manuscript.  
This research was supported by a grant (21 SCIP-B119958-06) from the Smart Civil Infrastructure Research Program funded by the Ministry of Land, Infrastructure and Transport of the Korean government. This research was also supported by the Institute of Construction and Environmental Engineering at Seoul National University. The authors wish to express their gratitude for the support.  
Not applicable.  
The data presented in this study are available in article.  
The authors declare no conflict of interest.