An apparatus for the plastic limit and workability of soils

Abstract

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 Tmax at the plastic limit can be derived together with other potentially useful properties such as the toughness limit wT, the moisture content at zero toughness, the toughness coefficients TC, the gradients of the relationships, the toughness index, the workability index and the stiffness transition.

Characterisation and undrained strength of amorphous clay

“…An important observation was that the bulk materials could be easily remoulded at water contents significantly below the measured PL values, which can be partly explained by scale effects for the Casagrande PL method (Barnes and O'Kelly, 2011), with the water content value at which crumbling occurs during rolling-out of the soil thread a function of the thread diameter. Hence the reported plastic range is notional, and, furthermore, the use of liquidity index as an indicator of the material's consistency is not reliable in practice.…”

Drying temperature and water content–strength correlations

“…Hence, if different researchers and (or) commercial laboratories consistently measure values of LL and PL using the same test methods and standardised procedures, but along with water content, these Atterberg limit values are based on different oven-drying temperatures, then the values of liquidity index will nevertheless bear a one-to-one correspondence. It is now widely accepted that strength values measured at the LL and PL states identified using the Casagrande percussion-cup and thread-rolling methods are not unique (see Barnes and O'Kelly, 2011;Haigh, 2012;Haigh et al, 2013). Hence, although usually quite sharp for a given material, ILN-log sur correlations can vary widely between materials.…”

Use of fall cones to determine Atterberg limits: a review

“…Attempts to improve on the standard PL test include the thread-rolling methods proposed by Gay & Kaiser (1973) and Bobrowski & Griekspoor (1992), a mechanically adapted version of the Bobrowski and Griekspoor's device (Temyingyong et al, 2002), and Barnes (2009Barnes ( , 2013aBarnes ( , 2013b. The Barnes' apparatus can measure indicative stress and toughness values for the soil thread during the rolling out procedure, with control of the strain rate, but the added complexity introduced into the test generally does not substantially alter the results obtained for PL.…”