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چکیده
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The effect of silt content on the undrained shear strength of sand-silt mixture has been experimentally investigated in the past three decades. These studies showed that, at the given confining pressure and global void ratio, the undrained shear strength decreases with increasing fines content. Between a threshold fines content and a limiting fines content, further addition of fines would lead to an increase of the shear resistance, where the behavior is controlled by both fine and coarse parts. Beyond the limiting fines content, the shear resistance will increase, and the behavior of soil is controlled by the fines content. On this basis, the state parameter of the equivalent intergranular void ratio is replaced by the global void ratio to describe the mechanical behavior of sandsilt mixture. In this study, a series of triaxial tests were performed on unsaturated sand-silt mixture with constant water (CW) conditions. Three levels of confining pressure and initial suction were considered. All specimens were prepared with the same equivalent intergranular void ratio to study its performance in the unsaturated state. The results of these tests showed that the suction effects on the soil strength are dependent on the fines content. For specimens with fines contents less than the threshold fines content or higher than the limiting fines content, the soil strength increased with increasing initial suction. However, for specimens with fines content between the threshold and limiting fines contents, the strength decreased with increasing initial suction. It was observed that the changes in volume did not have a definite relationship with the initial suction. The results also indicated that the application of the equivalent intergranular void ratio relations in the unsaturated state requires further considerations about the effect of matric suction.
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