结构性土压缩变形本构描述

Constitutively modelling the compression deformation of structured clay

在孔隙比与应力半对数坐标中,重塑土等向压缩线通常从正常固结线(NCL)下方逐渐趋近于NCL,整个过程中压缩线切线斜率大小单调增大。而对结构性土进行等向压缩时,因结构性的存在,压缩线会首先越至NCL之上,而后再从上方逐渐趋近于NCL,整个过程中压缩线切线斜率先增大后减小。重塑土与结构性土压缩线切线斜率演化在单调性方面的差异,可通过数学上增量函数构造的方法加以实现。如果在平面直角坐标系中以一水平线作为参考线,描述一过原点的函数曲线,使其上任意一处的切线斜率由该处函数值与参考线函数值的差决定,则参考线是否移动决定了所描述函数切线斜率演化的单调性。受此启发,在孔隙比与应力半对数坐标中提出移动正常固结线(MNCL)的概念。用MNCL代替NCL作为参考线,结合统一硬化模型(UH模型)的理论框架,建立了结构性土压缩变形的本构描述。

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.