A damage hypoplasticity constitutive model for cemented sand and gravel materials

A hypoplastic constitutive model is proposed to model the cementation-induced enhanced stiffness, strength and dilative behavior of cemented sand and gravel materials. The model is based on the original equations proposed by Gudehus and Bauer (1996) and is extended on the basis of the concept of geometrical constraints due to cementation. The novelty of the model is twofold. First, a damage-dependent additional void ratio term is added to the original equations for the maximum, minimum and critical void ratios to account for the geometrical constraints. As a result, the two-dimensional characteristic state lines are extended to three-dimensional characteristic state surfaces. Second, a new damage factor is introduced to the constitutive equation to reflect the effect of cementation on the peak strength, and the so-called barotropy component of the stiffness factor is reformulated. Both the additional void ratio and the damage factor are related to the damage process of the inter-particle bonds, and a strain-driven damage equation is proposed based on the results of previous discrete element simulations. The model is used to reproduce triaxial experiments on a cemented dense gravel and a cemented loose sand. It is capable of capturing most of the important features of cemented granular materials. The work described in this study demonstrates the capability of hypoplasticity in modeling the complex behavior of structured soils.