This paper focuses on a new approach for the definition of the tropical soil differentiation factor D, based on water retention parameters determined for 10 soil samples using a Richards's pressure extractor operating from 0 to 500 kPa suction. Two new differentiation factors, D_L and D_M were created using 36 tropical soil samples including the 10 initial samples. To obtain D_M) besides suction methodology, the following parameters of the Brazilian MCT-M methodology for tropical soils were used: c',d', Pi and e'. This methodology is based on MINI-MCV tests concerning compaction curves using disturbed miniature soil samples at different gravimetric water contents so as to permit full compaction. After MINI-MCV tests it is possible to classify the tropical soils in one of the three main following classes: Lateritic, Transitional and Non-Lateritic. The new factors D_L and D_M permit to differentiate Lateritic from Non-Lateritic soils so that D_L shows the variation suction tendency of the soil samples according to the improvement of their fine grain percentages.
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