Influence of soil suction on swelling pressure of bentonite-sand mixtures

Abstract

To investigate the effect of the changes in the soil suction on volume changes, expansion index, swelling pressure, shear strength and the coefficient of permeability, small-scale experiments were conducted on pure bentonite and bentonite mixed with sand with proportions of 30, 40 and 50% at different initial water contents and dry unit weights that were chosen from the compaction curves. In addition, large-scale model of soil with dimensions (700 × 700 × 650) mm was used to prepare the soil samples at the same initial water content and dry unit weight to show the effect of water content changes in different relations (swelling with time, swelling pressure with time, shear strength and soil suction). The results showed that the swelling potential decreases with increase in sand content from 14 to 2.4% by adding 50% sand to pure bentonite. 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 large scale model is 8.3% and from the conventional swelling test is 3.6% only. 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.