Influence of preparation techniques on the index properties of clay

Liquid limit (LL) and plastic limit (PL) are frequently used as indicators of the behaviour of fine-grained materials. These parameters are a prerequisite in every geotechnical investigation. Careful and consistent material preparation is a key component in the laboratory procedures adopted to determine the LL and PL. In preparing samples for such tests, various techniques are used in practice, and this paper examines the influence of these techniques on the actual magnitude of LL and PL measured. The index properties of a glaciolacustrine deposit, locally known as Belfast Upper Boulder Clay, which was laid down in glacial Lake Belfast, are examined. The index properties were determined on samples of the material prepared in different ways, including drying the material at two different temperatures (40°C and 110°C), crushing the dried material from coarse granular to fine granular form by adopting varying degrees of crushing effort, and mixing the dry material with both deionised water and tap water. The results indicate that the crushing procedure has a significant influence on particle size distribution and a consequential effect on the LL and PL. Pore water chemistry and the drying procedure also have a measurable influence on the magnitude of LL and PL.