Resilient and permanent deformation behaviour of clayey subgrade soil subjected to repeated load triaxial tests

Mechanistic-empirical design of flexible pavement AASHTO practice requires resilient characteristics of sub grade soil. Though the resilient modulus is assumed to account for plastic strain accumulation, some subgrade soils with more fine content undergo excessive plastic deformation under repeated loads even though they have remarkable resilient properties. Hence permanent deformation is also an important parameter which should be considered in the design process. In the present study, permanent deformation behaviour of clayey subgrade soil with intermediate compressibility is studied using repeated load triaxial tests. The influence of confining pressure, moisture content and deviator stress levels on the permanent deformation behaviour is examined. The transition of the soil sample from stable to unstable state can be observed and critical stress levels established with the help of shake down theory. Two regression models reported in the literature, Power law model and VTT model, are used to predict the plastic strains with a number of load cycles and stress levels as the variables.