Predicting the normalized, undrained shear strength of saturated fine-grained soils using plasticity-value correlations

Abstract

In soil mechanics, the plasticity of fine-grained soils is expressed using the plasticity index. This represents the difference between the water content at the liquid and plastic limits, which are often collectively referred to as the Atterberg (or consistency) limits. They are of key importance in soil mechanics because they determine, in a simple way, the interaction between the solid and liquid phases in soils, and thus provide the possibility to classify soils into groups with similar mechanical properties. As the Atterberg limits are the most distinctive and the easiest property of fine-grained soils to measure, several researchers have tried to use them to predict various mechanical properties, such as the normalized, undrained shear strength of fine-grained soils. The most widely used expression for predicting this value from the plasticity index was suggested by Skempton. Since then, there have been several studies to examine the validity of his relation. A lot of the data agree with this relation; however, there is an equally large volume of data that contradicts it. The present study shows that the correlation between the normalized undrained shear strength of cohesive soils and the plasticity index really exists, but it is not as simple as was suggested by previous studies. By considering the mineralogical properties of clay minerals and their impact on the quantity and state of water in soils, it was found that there is no uniform criterion to determine the normalized undrained shear strength from the plasticity index for all fine-grained soils.