Effect of Bentonite fine Content on the Triaxial Shear Behavior of Sandy Soils

Addition of fine and plastic clays such as bentonite to sandy soils is one of the methods of reducing soil hydraulic conductivity and making it suitable for seepage barriers. Also, in nature, soil mixtures such as clayey sands, silty sand and clayey silts are found much more than pure soils such as clean sand, clay or silt. Thus, in this paper, the effects of adding bentonite particles on the shear behavior of a sandy soil were studied by performing series of consolidated un-drained triaxial tests. In these experiments, different amounts of weight contents of bentonite such as 0, 5 and 10% were added to a sandy soil named Firoozkooh sand. Generally, obtained results showed that addition of bentonite led to changes in the shear behavior and strength of sand. These changes depend on the relative density of soil, confining stress and bentonite content. As an example, in loose samples of sand, addition of bentonite reduced the maximum deviator stress of the soil; on the other hand, in dense samples, addition of 5% bentonite reduced the deviator stress. However, addition of 10% bentonite increased the deviator stress. Generally, addition of bentonite reduced the secant modulus of elasticity and increased the positive pore water pressure at phase transition point. It is worth noting that, in dense samples, the effectiveness of bentonite content was not as high as that in loose samples and, in some conditions, the results did not follow a specific trend.