An indirect determination of the specific gravity of soil solids

The specific gravity of soil solids, Gs, is a significant material property in geomechanics. It is determined in the laboratory by water, gas or kerosene pycnometer, following a rather complex procedure. This Note suggests an original, simple and quick – albeit not empirical –method, which only requires knowledge of the soil unit weight γsat and the water content w in fully saturated conditions and allows one to obtain the soil solids specific gravity Gs as a derived quantity. The method can be also used for unsaturated soils, provided that they (or a paste made of the soil itself) are previously fully saturated. Gs values obtained applying this method to a variety of soils ranging from pure clays to fine-medium sands are in very close agreement with those determined using the pycnometer standard method. As a by-product, the method is a applicable also for assessing the in-situ unit weight of a saturated soil sample γsat, even of cohesionless fine-medium sandy soil, however disturbed it may be. The proposed method is not intended as a substitute for the standard pycnometer method, but as a simple and useful addition to the tool-bag for the characterization of ordinary soils.