Influence of Low Silt Content on the Anisotropic Behaviour of Sand

Most natural sandy deposits contain low amounts of fine content (< 10%), which is usually anisotropic and characterized by complex microstructures. The present study investigates the influence of low silt content on the anisotropic behaviour of sand. For this purpose, 30 undrained tests were performed using a hollow cylindrical apparatus with constant alpha degrees and b values on Firoozkuh sand. The specimens had silt contents of 0, 3, 5, 7 and 10%, and the inclination angle (alpha degrees) was varied from 15 degrees to 60 degrees. The specimens were prepared with the dry deposition method and subjected to confining pressures of 100 and 200 kPa. The equivalent intergranular relative density parameter was then introduced in order to create a comparative basis for the specimens. The experimental results show that increasing alpha leads to more contractive behaviour in the pure sand. By adding silt particles to the host sand up to 5%, the peak strength of the specimen is increased (18.5%, 12% and 7.7% for alpha = 15 degrees, 30 degrees and 60 degrees, respectively), and the strength of the specimen is decreased. It should be noted that with a silt content of 10%, the strength of the specimen was lower than that of the host sand (about 12%). On the other hand, it can be seen that with the increase of alpha, the influence of fine grains as an important parameter in sand-fine mixtures is decreased.