2015 Volume 71 Issue 4 Pages 301-316
A series of undrained cyclic tests were performed on sand-non plastic fines mixtures and sand-plastic fines mixtures with various fines content. The characteristics of a mixed soil depend on whether the fine grained or coarse grained material is the main constituent. The boundary of the area where coarse-grained soil formed the structural skeleton and the area where fine-grained soil composed the matrix was investigated. The consistency changed drastically on the boundary of a fines content of about Fc=20%~30%. From experimental results, the effect of the fines content Fc on the cyclic shear strength of both soils with the fine grained material forming the main constituent and soils with the coarse grained material forming the main constituent was considered. Through use of an equivalent skeletal void ratio which introduces a contribution factor b, a correction coefficient which takes the fines volume and course volume as the same, it became clear that there exists an unmistakable correspondence between the cyclic shear strength and the equivalent skeletal void ratio. Furthermore, with regards to the contribution factor b, it was found that the particle size ratio of the course and fine grained material correlated to some degree with the contribution factor b. From this, it was confirmed that the contribution factor b is important for evaluating the strength characteristics of mixed soils and an equation for predicting the contribution factor b using the particle size ratio χ is proposed.
