Determination of Atterberg Limits using the vane shear test method

Atterberg limits are important index parameters used to classify soils for various engineering applications. Engineering properties of soils are predicted through simple correlations with index properties and thereby the engineering behavior of soils are qualitatively assessed. There are two popular methods of determining liquid limit, and plastic limit is commonly determined adopting rolling thread methods. To avoid operator related variations in determining plastic limit by conventional method, some researchers have explored using cone method as an alternative. However, there is no consensus about the depth of penetration to reckon the end of plastic state. Though various other test methods have been developed to determine plastic limit (like roll plate device), cone penetration with its limitation of determining plastic limit, is the only method to determine both liquid and plastic limit of soils. Since laboratory vane shear test is a simple and reliable method of determining undrained strength of fine-grained soils, the authors have explored to determine both liquid and plastic limits through correlations developed between undrained strength and water content over a range of consistencies between liquid and plastic states. This would eliminate determining liquid and plastic limit separately without sacrificing the reliability of results.