The impact of different methods of Atterberg limits determination on the resulted Unified soil classification

One of the essential characteristics of fine-grain soils is the plasticity or Atterberg limits of them that directly are used in classification and prediction of mechanical properties and soil behavior. The aim of this study was to investigate the effect of different treatments of drying the soil sample on the plastic and liquid limits, type of measurement apparatus that used to determine liquid limit and the impact of these factors on the Unified soil classification. Also in this study, the results of the one-point method of Casagrande were compared with the usual multi-point method. For this purpose, soil samples were taken from three different forest types and five different depths in each type. The results showed oven drying of samples resulted in underestimation of the Atterberg limits and a different soil class in 33 percent of samples. Comparing the results of Casagrande and cone penetration apparatus to determine the soil liquid limit showed that the results were similar in both methods and only in one sample, there was different soil class. However, the cone penetration method is faster and requires less user experience. Finally using one-point method to determine the liquid limit, did not show difference with multi-point method and liquid limit differences between the two methods is about 0.26 percent; Which did not lead to significant displacement on the borders of Casagrande plasticity chart. Thus, in the case of sufficient experience and high number of samples, is recommended as an alternative to the usual multi-point method.