Behavior of Gravely Sand Using Critical State Concepts

A series of consolidated undrained triaxial tests were performed in order to understand the behavior of a gravely sand. The material was selected from Tehran alluvium and is classified as gravely sand in the Unified Soil Classification System. Critical state concepts were used for interpretation of the behavior of the soil. The critical state line in q-p'' space was reasonably unique. However, it was not possible to define a unique critical state line in e-ln p'' space. The overall scatter, in the critical state line for the gravely sand studied, was \pm 0.04, in terms of void ratio. Two reasons can be identified for this scatter. The first reason is the inevitable error in void ratio calculation and the second is that the behavior of this material, even at a critical state, is fabric and structure dependant. On the basis of these tests, it has been concluded that, for this material, a critical state zone with upper and lower limits can be defined. Nevertheless, a unique boundary surface can be defined by presenting the data in normalized stress space.