Experimental study on compressibility, volume changes, strength and permeability characteristics of unsaturated bentonite-sand mixtures

Expansive soils are generally found in arid and semiarid regions. These soils undergo volumetric changes upon wetting and drying, thereby causing ground heave and settlement problems. This characteristic causes considerable construction defects if not adequately taken care of. Solving the unsaturated soil problems needs the assessment of suction variation in time and space as a response to the variation of environmental factors such as rainfall and evaporation. To investigate the effect of the changes of the soil suction on the volume changes, expansion index, swelling pressure, shear strength and the coefficient of permeability, small scale experiments were conducted using pure bentonite and the bentonite mixed with sand in proportion of: 30%, 40% and 50% at different initial water contents and dry unit weights was chosen from the compaction curves. The study shows that the swelling-potential, swellingpressure, the soil-suction, the soil-strength and the coefficient of permeability are affected by the initial-conditions (water-content and dry-unit weight), where all these parameters except the permeability-coefficient marginally decrease with the increase in soil-water content, while the coefficient-of permeability increases with increasing the water-content