An elastic-viscous-plastic modeling of time-dependent behaviors of overconsolidated clays

The instant normal compression line is proposed by analyzing the existing theories and experimental results. Based on the creep law, the relationship between the aging time and the overconsolidation parameter is built. With the reloading equation of the UH model used to calculate the instant compression deformation, a one-dimensional stress-strain-time relationship is proposed. Furthermore, the characteristic rate that is a function of the overconsolidation parameter is defined. Then a three-dimensional elastic-viscous-plastic constitutive model is suggested by incorporating the equivalent time into the current yield function of the UH model. The proposed model can describe not only creep, rate effect and other viscous phenomena, but also shear dilatancy, strain softening and other behaviors of overconsolidated clays. Besides, it needs only one additional parameter (the coefficient of secondary compression) to consider the creep law compared with the modified Cam-clay model.