Evaluating plastic limit in vertisols with a drop-cone penetrometer

Abstract

The traditional thread and modified drop-cone penetrometer methods were used to evaluate the plastic limit of Vertisols (Typic Haplusterts). Quicker and more consistent results were obtained by a less experienced operator with the drop-cone penetrometer method, whereas the thread method required more time and an experienced operator. The plastic limits obtained with the thread method were lower than those obtained with the drop-cone penetrometer. Consistent results were obtained with the drop-cone penetrometer method by eliminating remolding of soils. This was done by using eight 30 mL plastic cups to which varying amounts of water had been added. Soil was then added to the cups. The soil water content (g 100g-1) was obtained from the top 10 mm of soil in each plastic cup. This depth was chosen as it was found to be the maximum depth to which the cone penetrated. It also eliminated the problem of a moisture gradient in the plastic cups. Show more