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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.

Bu çalışmada ASTM D4318-17 tarafından önerilen tek nokta likit limit saptama denklemindeki üstel katsayı Türkiye’de Doğu Karadeniz bölgesinde bulunan ayrışmış volkanik zeminler için belirlenmiştir. Numuneler 0.2 m ila 4 m derinliklerden, Rize’den 8 sahadan ve Trabzon’dan 1 sahadan alınmış olup toplamda 35 adettir ve bu numunelerle 77 adet Atterberg kıvam limitleri deneyi yapılmıştır. Bu çalışmada 3 farklı numune hazırlama yöntemi kullanılmıştır. Bunlar (1) herhangi bir ısıtmaya maruz bırakılmadan doğal su muhtevasından numune hazırlama, (2) 60C fırında kurutulduktan sonra hazırlama ve (3) 110C fırında kurutulduktan sonra hazırlamadır. Tek nokta likit limit saptama denklemindeki üstel katsayı, farklı yöntemlerle hazırlanan numuneler için hesaplanmış ve bu üstel katsayı ASTM D4318-17 standardında tavsiye edilen değer ile karşılaştırılmıştır. Bu çalışmada kullanılan zeminler Plastisite abağında ML-OL ve MH-OH sınıfında olup likit limit değerleri %35 ile %103 arasında değişmektedir (ıslak hazırlama yöntemi ile). Öte yandan çok nokta yöntemiyle belirlenmiş olan likit limit değerleri ile tek nokta yöntemiyle belirlenen değerlerin birbirine yakın olduğu görülmüştür. Sonuç olarak farklı numune hazırlama tekniklerinin üstel katsayı değeri 0.106 ila 0.133 arasında olup, ortalama değer olarak 0.120 elde edilmiş ve bu değerlerin ASTMD4318-17 de tavsiye edilen 0.121 değerine yakın olduğu görülmüş ve bu farklılıkların likit limit değerlerinde ihmal edilebilir bir farklılığa yol açtığı sonucuna varılmıştır (0-%2)., In this study, the power coefficient of one-point liquid limit equation given by ASTM 4318-17 is evaluated for weathered volcanic deposits of Northern Turkey. Total of 35 soil samples taken from depths ranging from 0.2 m to 4 m from 8 different sites in the city of Rize and one site in Trabzon, Turkey are used, and a total of 77 Atterberg limit tests are conducted. Three different sample preparation methods are used: (1) starting from in-situ moisture content without any drying, (2) drying at 60C oven, (3) drying at 110C oven. For liquid limit determination by one-point method, the best fitting power coefficient is evaluated for different sample preparation conditions separately, and are compared with the power coefficient suggested by ASTM D4318-17. Soils used in this study are in ML-OL to MH-OH zones in plasticity chart and the liquid limit values vary in the range of 35% to 103% (moist preparation). Liquid limits obtained by multi-point method and the ones obtained by one-point method are found to be similar to each other. It is concluded that although the power coefficient changes (in the range of 0.106 to 0.133 with an average value of 0.120) due to sample preparation technique, they are close to ASTM-suggested power value of 0.121, and the differences in resulting liquid limits are negligibly small (0-2%).