A Proposed Approach for Plastic Limit Determination Using the Drop-Cone Penetrometer Device

Abstract

The drop-cone method, in which a 30° cone of mass 80 g is allowed to penetrate into a soil sample at any moisture contents, was used to determine the plastic limit for more than 160 natural samples representing a wide range of soil type with different values of liquid limit ranging from 25 to 75%.Using the drop-cone penetrometer device, the moisture content corresponding at any penetration value is sufficient to generate the empirical formula to determine the plastic limit. The calculated values, from formula or chart, were close to the exact, tested, values. Hence, it is suggested to redefine the plastic limit as, the difference between the moisture content corresponding to the penetration of the drop-cone of 20 mm and that corresponding to any penetration divided by plastic factor corresponding to that penetration in which the product then subtracted from the liquid limit. The plastic factor can be determined from plastic factor-penetration curve. The advantages of such new method is that the test is more closely related to soil behaviour, less subjective, at least as reproducible as the Casagrande test and may be carried out simultaneously with the liquid limit test.