Constitutively modelling the compression deformation of structured clay

An isotropic compression curve of the remolded clay always approaches to the normally consolidated line (NCL) from below on the void ratio vs. logarithmic mean stress plane. In the whole process, the tangent value of the compression curve increases monotonically. While for the structured clay, due to the existing of internal structure, the compression curve firstly rises above the NCL and then approaches to the NCL from above. In the whole process, the absolute tangent value of the compression curve increases firstly and then decreases. The difference in the tangent evolution between the structured clay and the remolded clay can be analytically described through increment function. For example, a horizontal line in the rectangular coordinate system is made as the reference and a function starting at the origin is formulated through the tangent that is decided by the function value difference between the formulated line and the reference line. The monotonicity of the formulated function tangent depends on whether or not the reference line is static. Inspired by this, a moving NCL (MNCL) on the void ratio vs. logarithmic mean stress plane is presented considering clay structure effects. Taking the MNCL instead of the NCL to be the reference line and incorporating the framework of the unified hardening model (UH model), behaviors of the structured clay in compression are well modelled.