effect of nanoclay-depended treatment on the mechanical behavior of a collapsible soil

The research investigates the effects of adding nanoclay on the shear strength properties of two gypseous sand soils. the soil samples were taken from the cities of tikrit (55% gypsum) and al-najaf (29% gypsum). a direct shear test was used to examine soil specimens in dry conditions and immediately after a saturation procedure. the distributed soil specimens were remolded in the direct shear box to achieve a specific density. the shear speed was 1.0 mm/min. for both soil samples, there are different added nanoclay contents, 0, 2, 5, and 7%. three levels of normal stress are applied, 25, 50, and 100 kpa on each soil specimen. the results state that there is a significant decrease in the angle of internal friction with saturation for both soil samples due to the gypsum solution in these soils. the resulting saturated f is significantly lower than the reported mean values in the literature. the f is recovered by adding nanoclay content up to 5% worthily. a mathematical model correlates the values of f and the percentage of nanoclay using a regression analysis with restricting gypsum content (29-55%) and nanoclay (≥ 0%) in saturation conditions.