Critical-state parameters of an unsaturated residual clayey soil from Turkey

This paper deals with the evaluation of the critical-state parameters with respect to the matric suction for saturated and unsaturated undisturbed residual clayey soils from Turkey. In order to conduct the unsaturated triaxial compression testing procedures a conventional triaxial compression apparatus was redesigned. The data for critical-state conditions from these tests are presented with respect to matric suction, based on the critical-state parameters of M, qo, Γ, λ, which is commonly proposed by many authors. The critical state of the unsaturated samples is compared with that of the saturated samples. This experimental study has demonstrated that matric suction has no influence on parameters of M and λ. The parameters of M and λ are approximately 0.85 and 0.074 respectively for saturated and unsaturated conditions. The relationships between matric suction (ua − uw) and the intercepts qo and Γ have been observed as nonlinear, and thus they can be defined as a function of matric suction (ua − uw). Furthermore, a method is developed to predict the intercepts q0 according to matric suction for unsaturated clayey soils.