## 1 Introduction  
Granite is frequently encountered in South Korea, and its weathered layers are generally distributed. For general engineering purposes, their weathering grades are usually classified into six grades from fresh rock to residual soil [1]. Grade IV (highly weathered) and V (completely weathered) granite that preserves the texture and structure of the parent rock is developed in South Korea, and thus, various structures are constructed on the weathered granite; therefore, it is important to evaluate the shear strength of grade IV and V granite for a reasonable and rigorous design to secure the performance and safety of the structures; however, it is quite difficult to obtain reliable shear strength parameters because of the intrinsic characteristics of the weathered granite. [PERSON] [2] reported that soil and rock testing devices used to evaluate geotechnical properties are not appropriate for application to grade IV and V granite, as it has intermediate strength between soils and hard rocks, which is sometimes too low or too high for the rock or soil testing devices. For example, for the high strength of grade IV and V granite, the standard penetration test (SPT) has its limitation, as the penetrability of SPT is not sufficient and typical \(N\) values are greater than 50, which is not generally recommended for interpretation. Moreover, [PERSON] and [PERSON] [3] reported that SPT can lead the uncertain and insensitive site characterization for the ground with hard residual soil, soft rock, and fractured rock. In the view of laboratory tests, which requires sampling, the sample extraction process commonly destroys cores of grade IV and V granite even though the triple-core barrels are adopted. For grade IV and V granite, the pressuremeter test (PMT) has been one of the most appropriate in situ test methods; it has been applied for both soils and unusual geomaterials such as weathered or fractured rock, cemented soil, and frozen soil [4; 5; 6; 7; 8; 9]. After analysis test results from the PMT, cone penetration test (CPT), SPT, and laboratory tests (after sampling process) from 204 sites, [PERSON] et al. [9] concluded that PMT is the most versatile in situ test for weathered or fragmented rocks. Additionally, [PERSON] et al. [5] analyzed the friction angles of the Hong Kong granite saprolites including grade IV and V granite using the self-boring pressuremeter (SBPM) test results and [PERSON] and [PERSON] [8] performed the SBPM on many types of weathered rock and presented their friction angles. There have been research studies to figure out the relationship between the strength parameters and the chemical weathering indices for weathered rock [10; 11; 12; 13; 14; 15]. [PERSON] [10] and [PERSON] [12] showed that there was a linear relationship between the dry density and a mobile index (\(I_{mob}\)) for Hong Kong granite. [PERSON] and [PERSON] [11] reported linear relationships between the various weathering indices and the unconfined compressive strength (UCS) for Cavusbasi granitic rocks in Turkey. [PERSON] and [PERSON] [13] investigated the correlation between dry density, UCS, and chemical weathering indices for artificially weathered granite. However, these studies have focused on grade I-III rocks, of which an intact core sample is relatively easily obtainable. On the other hand, [PERSON] et al. [16] estimated engineering properties of grade IV and V granite based on chemical weathering indices. [PERSON] et al. [16] assessed that four chemical weathering indices (Vogt's ratio, modified weathering potential index, chemical index of alteration, and mobile index) and found that the their correlation with pressuremeter modulus (\(E_{m}\)) shows a strong relationship (R\({}^{2}\) > 0.7). However, shear strength parameters (e.g., friction angle), which are important to a geotechnical design, have not been not considered seriously with sufficient field data.