Fall-cone testing of unsaturated sand–clay mixtures

This paper presents the results of an intensive series of laboratory fall-cone tests undertaken on mixtures of sand with different grain size/shapes and a low-plasticity clay. The mixtures were prepared with various water contents from a fully dry to a fully saturated condition. The clay was added to two different gradations (0·15–0·30 mm and 1·0–2·0 mm) of clean sand with specific shapes (rounded and angular) at the ratios of 5, 10, 15, 20, 30 and 40% by dry weight. The results obtained suggest that penetration depth primarily depends on water content, size/shape of the sand grains and the amount of clay in the mixtures. The relation between penetration depth and water content displays three distinct behaviours in that the penetration depth (a) is relatively large for dry mixtures, (b) decreases with increasing water content, and (c) increases to values approximately 20% larger than those for dry mixtures. Observations revealed that the transition fines content, the boundary between sand-governed and fines-governed behaviour, was mainly affected by intergranular void ratio.