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Index Properties and Classification of Marginal Fills or Coarse-Fine Mixtures

Huvaj Sarıhan, Nejan
Ekici, Anll
Ekici, Anll
Akgüner, Cem
© 2019 American Society of Civil Engineers.The behavior of soil under loading is strongly influenced, and in some cases governed, by the relative percentage of coarse and fine particles. There are many intermediate graded soils whose response simply cannot be explained by "granular (non-cohesive)" versus "clayey (cohesive)" soil behavior. These soils have been commonly referred to as marginal fills. The limiting fines content when soil behavior changes from coarse-grained to fine-grained-dominated (i.e. fines fraction corresponding to a given behavioral threshold) is critical for developing a better understanding and more effective design decisions. Soil classification systems are beneficial in grouping soils into similar behavioral categories. Yet, there are limitations/drawbacks in currently utilized classification systems, when it comes to classification of marginal fills, since they fail to capture the dominant role of fines on the mechanical and hydraulic properties of soils. In this study, a total of ten sandy soil mixtures with 0%, 12%, 20%, 30%, and 40% fines, and plasticity indexes of 5% and 15% were prepared in the laboratory by mixing different proportions of coarse and fine sands, non-plastic silt, kaolin, and bentonite. All index properties including grain size distribution curves, Atterberg limits, maximum and minimum void ratios, maximum dry density, and optimum water content were determined. The mixtures were classified according to USCS, AASHTO, and revised soil classification system. Comparisons of different classification systems and their limitations were demonstrated for these marginal soils.