Behavior and characteristics of compacted expansive unsaturated bentonite-sand mixture

Abstract

Limited studies dealt with the expansive unsaturated soils in the case of large-scale model close to the field conditions and therefore, there is much more room for improvement. In this study, expansive (bentonite–sand (B–S) mixture) and non-expansive (kaolin) soils were tested in different water contents and dry unit weights chosen from the compaction curve to examine the effect of water content change on soil properties (swelling pressure, expansion indices, shear strength (soil cohesion) and soil suction) for the small soil samples. Large-scale model was also used to show the effect of water content change on different relations (swelling and suction with elapsed time). The study reveals that the initial soil conditions (water content and dry unit weight) affect the soil cohesion, suction and swelling, where all these parameters slightly decrease with the increase in soil water content especially on the wet side of optimum water content. The settlement of each soil at failure increases with the increase in soil degrees of saturation since the matric suction reduces the soil ability to deform. The settlement observed in B–S mixture is higher than that in kaolin due to the effect of higher swelling observed in B–S mixture and the huge amount of water absorbed which transformed the soil to highly compressible soil. The matric suction seems to decrease with elapsed time from top to bottom of tensiometers due to the effect of water flowing from top of the specimen. The tensiometer reading at first of the saturation process is lower than that at later period of saturation (for soil sample B–S3, the tensiometer #1 took 3 d to drop from 93 kPa to 80 kPa at early stage, while the same tensiometer took 2 d to drop from 60 kPa to 20 kPa).