Comparison of Liquid Limit of Soils Resulted from Casagrande Test and Modificated Cone Penetrometer Methodology

In this paper the experimental work in the field of evaluation the liquid limit is described. Two different types of soil were analyzed – loam (intermediate plasticity) and sodium bentonite (high plasticity). Two basic methods were used for the evaluation of the liquid limit – Casagrande percussion (cup) method and cone penetrometer method. Two approaches were applied to the evaluation of liquid limit based on cone penetrometer test (30°/80 g cone) – standard method assuming 20 mm penetration at liquid limit and new calibration line for cone penetrometer liquid limit - NCCLL (Mohajerani). Experimentally obtained calibration line assumes the influence of depth of cone penetration at liquid limit on undrained shear strength, which is not unique for all types of soils. The paper presents the comparison of results of liquid limit based on the previously mentioned methods. Presented results of laboratory tests show, that bentonite liquid limit based on the standard cone penetration test (using 20 mm penetration) is significantly lower in comparison with Casagrande liquid limit. On the other hand was verified very significant consistency of Casagrande liquid limit and liquid limit based on NCCLL (evaluated depth of penetration 29 mm). Obtained results indicate the need for further research in this area.