Effect of porewater salinity on residual shear strength of clays and their mixtures

Abstract

Abstract It has been long recognized that the residual shear strength of clayey soil is influenced by porewater chemistry due to physico-chemical interactions between clay and porewater. However, although the correlation between the residual shear strength of clayey soils and salinity of porewater has been discussed by many researchers, it has not been quantitatively specified either in theory or experiment. In this study, the residual shear strength of pure and mixed clays made of smectite, interlayered illite/smectite and kaolinite were investigated after being saturated with NaCl solutions of various concentrations. It was found that the residual shear strength of smectite significantly increased when the concentration of the NaCl was in the range of 0–1 mol L−1 and showed little change when the NaCl concentration was higher. The residual shear strength of kaolinite displayed insignificant change when NaCl concentration varied. Variation of the residual shear strength of interlayered illite/smectite with porewater salinity was quite similar to that of smectite, but with much less magnitude. Moreover, the residual shear strength of the clay mixtures also displayed great variation with the porewater salinity, and the variation may be mainly attributed to aggregation when porewater salinity varied as a result of change in double-layer thickness among clay particles.