A Re-Examination of Alternative Test Procedures for Soil Consistency Limit Determination: II. A Simulated Desorption Procedure
1989
McBride, R. A.
A soil water retention model was used to simulate a desorption procedure for Atterberg consistency limit determination (i) to test the validity for Ontario soils of this procedural alternative to the A.S.T.M. standard methods in light of past research efforts, and (ii) to allow for the assessment of soil plasticity and related soil qualities for soil inventory interpretive purposes with only a minimum of soil physical data. From a remoulded and effectively saturated initial condition, the upper and lower plastic limits of the 290 soil horizons investigated were generally found to occur at the upper and lower flex points, respectively, of the estimated moisture retention curve. The presumed absolute equivalence of the effective normal stress required to bring soils to their respective Atterberg consistency limit moisture contents in a compression-based test procedure with the negative pore water pressure potential at the estimated moisture characteristic flex points was corroborated. The observed tendency to underestimate the A.S.T.M. lower plastic limit of low clay content (marginally plastic) soils was attributed to procedural limitations in the A.S.T.M. standard methods which set the lower moisture content limit of plasticity of such soils unrealistically high. Clay and organic matter contents influenced both the effectively saturated gravimetric moisture content attained by free swelling soils in a remoulded condition and the pore water pressure potential at the lower plastic limit. Only clay content was a significant factor in explaining variations in pressure potential at the upper plastic limit with soil texture.
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