Estimation of in situ geotechnical properties on highly weathered granite using chemical weathering indices

Highly weathered granites exist in thick subsurface layers in most regions of South Korea and are often used as a bearing stratum of geotechnical structures. However, because of the difficulty of retrieving samples for laboratory tests and the cost and time constraints of in situ testing, researchers mostly estimate the geotechnical properties of highly weathered granite using the standard penetration test (SPT)-N values or directly adopt the literature values. In this study, in situ testing was performed to evaluate the geotechnical properties of highly weathered granite in South Korea, and the chemical weathering indices were calculated using the retrieved samples. Particular attention was given to the development of a geotechnical properties estimation method that could consider the degree of weathering and site-specific characteristics using both in situ test results and chemical weathering indices. Correlation analysis was performed between the geotechnical properties of the highly weathered granite predicted by the proposed method and the measured geotechnical properties. The results show that the pressuremeter modulus values (E_m and E_ur) that were estimated using the modified weathering potential index (MWPI) showed a strong correlation (R² > 0.7) with the measured values.