Dynamic Bounding Surface Viscoplasticity for Clays

Experimental evidence has demonstrated that time-dependent behavior of clays significantly relates to the overconsolidation ratio, which could not be comprehensively predicted by current overstress-based models. This paper first proposes the rate-dependent dynamic bounding surface with deriving a new overstress function related to the ratio of reference stress to dynamic bounding stress according to a unique stress–strain–strain-rate relationship. Next, a nonassociated flow rule related to the ratio of critical void ratio to current void ratio, along with a hardening modulus related to the overconsolidation ratio, is proposed for the dynamic loading surface to account for the dilatancy characteristic. Different from the literature, this novel elastic-viscoplastic modeling approach, so-called dynamic bounding surface viscoplasticity for both normally consolidated and overconsolidated soils, is thus developed. Finally, the model’s predictive performance is successfully evaluated by comparing experimental and simulated results of a series of time-dependent tests on clays with different overconsolidation ratios.