Through the hydrostatic compacting tests, it has been possible to evaluate the compression index Cc, that is the soil compaction index. Generally, the parameter Cc is affected by the soil granulometry composition and moisture content. In this paper, they have been examined 24 soil typologies representative of almost all types of sandy soils, to determine the compression index (Cc) denoting the soil compaction capability, and alterations in the Cc value when soil granulometry composition and moisture change. The soil samples were submitted to a hydrostatic compression test (HCT). Pressure-void index (p-e) diagrams were obtained, from which the compression index (Cc) was determined using the Gompertz model. The modulus of the slope of the virgin compression curves – the compression index (Cc) – were estimated as the modulus of the slope at the first inflection point of the Gompertz curve. The Gompertz model parameters were evaluated using a nonlinear regression method. The model fit the raw data closely, with mean R2 values greater than 0.99. The results reveal how the Cc index changes when the granulometry and humidity values change. Further, the experimental data 3D diagrams provide a better description of the mechanical behaviour of a family set of soils.

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