Relationships between chemical weathering indices and physical and mechanical properties of decomposed granite

• Chemical, physical and mechanical properties of decomposed granite are studied.
• Mobiles index is correlated to dry density, fines content and maximum dilatancy.
• Rowe's stress–dilatancy can model peak states of granitic saprolites.

Chemical weathering is one of the dominant mechanisms for weathering of granite in subtropical and tropical regions resulting in modifications of its chemical, physical and mechanical properties. Thus, the changes in chemical properties may provide insight about the changes in physical and mechanical properties of weathered granite. In this paper three quantitative chemical weathering indices are correlated to the dry density of decomposed granite. A linear relationship is found between each chemical weathering index and dry density for granitic saprolites. Mobiles index (Imob) gives the highest coefficient of correlation among the three chemical weathering indices. Further investigations were conducted to establish the relationships between Imob and other physical and mechanical properties of granitic saprolites. The test results showed that fines content increases with increasing Imob, but peak strength increases with decreasing Imob. The peak states of granitic saprolites are consistent with Rowe's stress–dilatancy relationship. Dilatancy increases with decreasing Imob that contributes to a higher peak strength. Based on some test results presented in this study, it seems that Imob could be a good indicator to quantify the effects of chemical weathering on physical and mechanical properties of granitic saprolites.