A double-structure formulation of NCL for saturated bentonite differentiating free and adsorbed water

The normal consolidation line (NCL) of saturated bentonite is not a unique straight line in the semi-logarithmic coordinate, but depends on the initial structure formed during the hydro-mechanical processes experienced. This phenomenon differs from that of common saturated remolded clays and also has not been considered in the existing constitutive models for bentonite. In this study, measured compression curves for the saturated bentonite specimens with different initial structures resulted from different hydro-mechanical processes were analyzed. Results show that NCLs are different in the free water-dominated region, while tending to coincide in the adsorbed water-dominated region. Accordingly, two compression mechanisms corresponding to the clay-water properties of free water and adsorbed water of saturated bentonite have been explored. Then, a double-structure formulation of NCL for saturated bentonite was developed to reflect the coupling effects of two compression mechanisms. Finally, the proposed formulation was validated by simulating the compression tests carried out on several bentonites followed different stress paths. Results confirmed that by introducing the coupling effects of two compression mechanisms, the proposed formulation is capable of providing a unified description NCLs of saturated bentonite with different initial structures. The NCL formulation proposed in the work could be used for development of double-structure constitutive models for bentonite.