A Constitutive Model for Structured Soils Based on HISS Model and Disturbed State Concept

The compression behavior of structured soils after virgin yielding is nonlinear that can not be captured by a single line in semi- ogarithmic or fully-logarithmic stress-volumetric strain space. Increasing the stress level from the threshold stress of the virgin yielding initiates the crashing of the soil structure. Further crashing the structure of the soil and decreasing its void ratio increases the volumetric stiffness of the soil. Although this procedure is highly nonlinear, however it is a continuous phenomenon and can be formulated mathematically. Since the structure losing behavior of structured soils occurs between two known states, therefore, could be explained based on the disturbed state concept (DSC). According to the DSC, the behavior of complex phenomena between two reference states could be described based on their behaviors in two reference states using an appropriate state function.In this paper a constitutive model base on hierarchical single surface model (HISS) and the disturbed state concept was proposed to describe the stress-strain and the failure behavior of structured soils. The behavior of the soil at the beginning of the virgin yielding was considered as initial, relatively intact (RI), state and its behavior after fully crashed state was considered as fully adjusted (FA) state. A power form state function was proposed to describe the variation of the bulk modulus of the soil. The variable compression model was implemented in HISS model to capture the volumetric behavior of the structured soil. The proposed model verified based on the data from literature.