Fall cone tests on clay–sand mixtures

• The cone penetration and water content for clay-NS/CSS mixtures has about linear relationship.
• Shape and gradation of the sands can contribute differently to the LL values.
• As the amount of sand in a clay matrix increases, LL and su values decrease.
• Use of rounded shape grains result in a slightly higher su.
• Gradation of the sand grains has no effect on the su.

Fall cone tests were performed on clay–sand mixtures to investigate the variation of liquid limit with sand content and the link between undrained shear strength and water content for various sand contents in the mixtures. Five different particle gradations (4.75–0.075 mm, 4.75–2.0 mm, 1.18–0.6 mm, 0.6–0.075 mm, and 0.425–0.3 mm) of sands having distinct shapes (rounded and angular) were added to a low plasticity clay with mixture ratios of 0%, 10%, 20%, 30%, 40%, and 50%. Data of the clay–sand mixtures showed that the depth of cone penetration against water content relationship is about linear. The liquid limit estimates of the mixtures were measured to be slightly affected by the gradation and shape of the grains in the range of sand contents employed. The obtained results indicated a decrease of undrained shear strength with an increase in the amount of sand. The use of rounded sands in a clay matrix leads to the development of higher undrained shear strength values, on which gradation of the sands has no effect.