The critical state (CS), the anchor concept in the critical state soil mechanics (CSSM) framework, has been comprehensively evaluated in triaxial stress conditions, where all the principal stresses are known but the pure shear stresses in the shear directions are absent. Therefore, the evolution of first and second invariants of the stress tensor (σ′) i.e. the mean effective stress (p′) and deviatoric stress (q) along with volumetric strain (${\epsilon }_v)$ is often used to identify the CS. However, the same does not apply for a direct simple shear (DSS) test, which is more representative of the real ground condition, as in most cases the minor principal stresses are not measured. This leads to the challenge of determining the CS line in the $e-\mathrm{l}\mathrm{o}\mathrm{g}(p^{\text{'}})$ space and thus the concept of state parameter ($\psi$) cannot be used to characterise soil behaviour. Using DEM, this study evaluates CS for DSS, using evolution σ′ and ${\epsilon }_v$, in the $e-{\sigma \text{'}}_N$ space, compare its location with triaxial CS lines in the $e-\mathrm{l}\mathrm{o}\mathrm{g}(p^{\text{'}})$ space. The CS line for DSS in $e-{\sigma \text{'}}_N$ space was then used to define a modified state parameter, $\psi$, (${\psi }_m$). It was found that both $\psi$ and ${\psi }_m$ showed good correlations with characteristic behaviour e.g. onset of liquefaction, phase transformation state, fabric anisotropy etc. Therefore, ${\psi }_m$ maybe a good alternative of $\psi$ for DSS test where the minor principal effective stresses are not measured to define a CSL in $e-\mathrm{l}\mathrm{o}\mathrm{g}(p^{\text{'}})$ space.

临界状态 (CS) 是临界状态土力学 (CSSM) 框架中的锚固概念，已在三轴应力条件下进行了综合评估，其中所有主应力已知，但剪切方向上的纯剪应力不存在。因此，应力张量 ( σ' )的第一和第二不变量即平均有效应力 ( p ') 和偏应力 ( q ) 以及体积应变 (${\epsilon }_v)$常用于识别 CS。然而，这不适用于直接简单剪切 (DSS) 测试，它更能代表真实的地面条件，因为在大多数情况下不会测量次要主应力。这导致确定 CS 线的挑战$\mathrm{电子}——\mathrm{升}\mathrm{○}\mathrm{G}({磷}^{\text{'}})$ 空间以及状态参数的概念（$\psi$) 不能用于表征土壤行为。本研究使用 DEM 评估 DSS 的 CS，使用演化σ'和${\epsilon }_v$，在$\mathrm{电子}——{\sigma \text{'}}_N$ 空间，将其位置与三轴 CS 线进行比较 $\mathrm{电子}——\mathrm{升}\mathrm{○}\mathrm{G}({磷}^{\text{'}})$空间。DSS 中的 CS 线$\mathrm{电子}——{\sigma \text{'}}_N$ 然后使用空间来定义修改后的状态参数， $\psi$, (${\psi }_{米}$）。结果发现两者$\psi$ 和 ${\psi }_{米}$ 表现出与特征行为的良好相关性，例如液化开始、相变状态、织物各向异性等。因此， ${\psi }_{米}$ 也许是一个很好的选择 $\psi$ 用于 DSS 测试，其中不测量次要主有效应力来定义 CSL $\mathrm{电子}——\mathrm{升}\mathrm{○}\mathrm{G}({磷}^{\text{'}})$ 空间。