Behavior of Clay-Sand Mixtures under Undrained Triaxial Conditions

Previous studies on the behavior of clayey soil mixed with granular materials shows that major researches has been done under low confining stress level so that they almost exhibit behavior similar to normally consolidated clayey soils and by increasing content of granular materials both of the shear strength and excess pore water have been raised. In some researches, the results are inconsistent and the effect of grain size of granular materials is not clear. To study the behavior of these soils comprehensively, a series of consolidated undrained triaxial tests carried out on the clay and clay – sand mixtures under a wide range of confining stresses. The results show that the behavior of these soils depends on sand content and grain size. Adding 60% sand to clay, the shear strength increases and the mixtures consist of fine sand has lower strength in comparison with those of including coarse sand. It also observed that dependent on content and size of sands, the behaviors of specimens change from contractive to dilative one. So that at low confining stresses, by an increase in sand content from 0% to 60%, the behavior of samples change from contractive to slight dilation and then it is observed heavily dilation at samples include 60% sand.