Influence of fines content on the undrained cyclic shear strength of sand-clay mixtures

A series of undrained cyclic triaxial tests were performed on sand-clay mixtures with various sand-clay mixing ratios. Prior to the primary tests, the threshold fines content was examined by consistency tests, which was found to be approximately 20%. For sand-clay mixtures with a sand-matrix (fines content less than the threshold fines content), the cyclic shear strength of low-density mixtures increases and that of high-density mixtures decreases with increasing fines content. However, for sand-clay mixtures with a fines-matrix (fines content greater than the threshold fines content), there exists a unique correlation between the cyclic shear strength and global void ratio for different fines content. The equivalent granular void ratio is introduced in this paper to account for the contribution ratio of the fines to soil skeleton. As a result, a unique relationship between cyclic shear strength and equivalent granular void ratio was observed for pure sand and sand-clay mixtures with a sand-matrix.