An essential hypothesis is that the flow failure landslides occurring in the Chinese Loess Plateau may initiate in the high-moisture-content loess in the capillary zone rather than in the saturated zone within the slope. Two effective stress paths, namely, the monotonically increasing loading and wetting-based constant loading under undrained conditions, are performed on intact and mechanically compacted loess, aiming at specifying their hydromechanical trajectories when subjected to an increasing water content. The results indicate that static liquefaction is initiated when the soil moisture reaches a threshold during the wetting process after exhibiting a sharp increase in pore water pressure accompanied by strain-softening behavior. Accordingly, we define this state as the initiation of flow failure under the unsaturated framework to distinguish it from static liquefaction, and first propose its corresponding critical mechanics and criterion. Its validity and physical justification are mainly evidenced by the following observations: i) Significant difference in the pore characteristics of the test samples before and after flow failure initiation; ii) Approximate equivalence between the measured and predicted hydromechanical thresholds at the flow failure initiation state; iii) Existence of the strength envelope corresponding to the flow failure initiation state; and iv) The uniqueness of the modified critical state line in the full suction range. This paper provides a general approach to accurately identify the flow failure potential for unsaturated loess, especially in the capillarity zone within a slope, which is of vital importance to the early identification and risk mitigation of loess landslides with a fluidization pattern.

一个基本的假设是，黄土高原地区发生的流失性滑坡可能始于毛细带高含水量的黄土，而不是斜坡内的饱和带。在完整的和机械压实的黄土上执行两条有效应力路径，即在不排水条件下单调增加荷载和基于湿润的恒定荷载，旨在确定当水含量增加时它们的水力力学轨迹。结果表明，在润湿过程中土壤水分达到临界值后，孔隙水压力急剧增加并伴随着应变软化行为，从而开始了静态液化。因此，我们将这种状态定义为在非饱和框架下流动破坏的开始，以将其与静态液化区分开来，并首先提出其相应的临界力学和判据。其有效性和物理合理性主要由以下观察结果证明：i）流动失效引发前后，试样的孔隙特性存在显着差异；ii）在流失起始状态下测得的和预测的水力机械阈值之间的近似等效值；iii）存在与流动破坏开始状态相对应的强度包络线；iv）修正的临界状态线在整个吸力范围内的唯一性。本文提供了一种通用方法，可以准确地识别非饱和黄土的流动破坏潜能，