Formulation of a general gradation curve and its transformation to equivalent sigmoid form to represent grain size distribution

This paper proposes the trunk-additive equation to represent grain size distribution (GSD) also called particle size distribution (PSD). The general form of the equation used in research can be transformed to the sigmoid form observed in granular production. Proposed equation covers the whole granulometric canvas from powders but mostly from silts to large open-graded curves. This paper also illustrates some of the capabilities of the trunk-additive equation. Proposed equation of GSD allows staying as close as possible to the maximum density curve while truncating fines in order to create a gap to release pore pressure and increase drainage. Proposed equation also represents addition of fines particles to study clogging or plasticisation. When combining two or more of these curves, one creates bimodal or multimodal curves.