Swelling Behavior of Unsaturated Expansive Soil

Abstract

To investigate the effect of the changes of the soil suction on volume changes, small-scale experiments were conducted for pure bentonite and bentonite mixed with sand of proportion 30%, 40%, and 50% at different initial water contents and dry unit weights that were chosen from the compaction curves. In addition, a large-scale model with soil dimensions 700 × 700 × 650 mm was used for the same initial water content and dry unit weight to show the effect of water content changes on swelling with time and soil suction. It was concluded that the swelling potential decreases from 14 to 2.4% with an increase of sand content by adding 50% sand to pure bentonites. The swelling percent found from the large-scale model is higher than that obtained from the oedometer swelling test for the same soil. This result applies well on BS5 (50:50, bentonites:sand) soil sample for which the swelling potential from the large-scale model is 8.3% and from the conventional swelling test is 3.6%. The measured swelling pressure from the swelling test at small soil samples is much higher than that measured from the large-scale model. For soil sample BS3 (60:40, bentonite:sand), the swelling pressure decreases from 50 kPa in the swelling test to 23.2 kPa in the large-scale model. The swelling potential decreases with an increase of the soil suction for all types of soil subjected to different periods of saturation.