2023 Volume 64 Issue 4 Pages 183-198
The author has proposed the following chemical weathering index （CWI, abbreviated name Sueoka’s Index） as an index that enables the degree of chemical weathering and the chemical weathering direction to be quantitatively evaluated simultaneously for granitic residual soils that are found throughout the world.
CWI = [Al2O3 + Fe2O3 + TiO2 + H2O(±)(mol%)/Total chemical components (mol%)]×100（％）
In this Report （Part 1）, the chemical weathering index CWI is used to clarify composition in accordance with the combination of the chemical components based on the mobility of the chemical components, and the significance and effectiveness of the CWI and its meaning for today’s issues are discussed. From the results it is shown that the extent and direction of chemical weathering of granitic residual soils can be quantitatively expressed using both the CWI value and the position in triangular coordinates of the three chemical component groups of which the CWI is composed.
In addition, using the CWI, definitions have been established for terminology related to weathering products, such as weathered granite, Masado （decomposed granite soil）, saprolite, and lateritic soils, laterite, and geomechanical classification of residual soil grounds incorporating rock mass classification have been established.
