The mineralogical and chemical controls upon the residual strength of pure and natural clays

Recent work has shown that the residual strength of clays is, to a large extent, determined by the type of clay minerals and the chemistry of the constituent pore water. Changes in either of these factors cause corresponding alterations in residual shear strength. The findings have important implications for the seasonal reactivation of landslides and may also provide an explanation for the long-term weathering and shear strength reduction of clay slopes. Results are presented here to demonstrate the separate effects of clay mineralogy and pore water chemistry upon the residual strength of pure and natural clays. Explanations are sought to identify the controls of these factors upon residual strength based on brief reviews of the shear strength and physico-chemical behaviour of clays. The findings strongly suggest that residual strength should be considered a dynamic property, with increases or decreases in strength occurring in response to environmental change.