Properties of Slightly Organic Topsoils

The effect of small increases in organic content on the classification and engineering properties, such as specific gravity, Atterberg limits, compaction, and compressibility, of several natural soils and slightly organic soil mixture is investigated; emphasis is placed on slightly organic cells, as opposed to highly organic soils, such as peats and muck. The specific objective of this study is to provide the engineer in charge of construction or inspection, or both, with improved guidelines for determining the engineering suitability of slightly organic topsoils. The organic burn or loss on ignition test was found to be not generally reliable for use on slightly organic soils, and an H2O2 digestion procedure is proposed as an index of organic content. Increasing the organic content of a soil is found to increase both the Liquid Limit and the Plasticity Index, with a significantly greater increase in the Liquid Limit. Also, if the organic content is around 0.5 % to 1.0 % according to the H₂O₂ digestion test, significant differences in compaction and compressibility characteristics occur with only a slight change in the organic content.