An apparatus for the plastic limit and workability of soils

An apparatus is described that replicates Atterberg's rolling technique for the determination of the plastic limit of soils by detecting the brittle–plastic transition. There is much less operator interference, and judgement of the crumbling condition is practically eliminated. In addition, by means of a loading device, stresses are applied during rolling, the diameter is measured for each rolling traverse, and plots of stress against strain are derived. The workability or toughness of the soil is determined as the product of stress and strain, or work/unit volume, for soil threads prepared at moisture contents ranging from near the sticky limit through the workable plastic region to the brittle state. From the results an abrupt brittle–plastic transition is found, allowing the plastic limit to be defined as the moisture content at this transition. Good relationships between toughness and moisture content are obtained, from which the maximum toughness T_max at the plastic limit can be derived together with other potentially useful properties such as the toughness limit w_T, the moisture content at zero toughness, the toughness coefficients T_C, the gradients of the relationships, the toughness index, the workability index and the stiffness transition.