Loess–Fiber Interfaces in Direct Shear: An Energy‐Consistent Traction–Separation Framework for Parameter Identification

ABSTRACT Accurate assessment of deformation in fiber‐reinforced loess requires a reliable contact‐scale traction–separation law. Predictive accuracy hinges on interfacial parameters, yet estimates derived from single‐fiber pull‐out tests are not representative of the in‐situ Loess–fiber interaction. This study formulates a three‐dimensional finite‐element micromechanical representative element with a single fiber embedded in loess, where the Loess–fiber interface obeys a traction–separation law combining cohesive bonding and frictional sliding, reproducing the interface's shear‐stress‐displacement response and cumulative frictional dissipation. Within an energy‐dissipation framework, cohesive parameters were obtained from test‐derived Mode II work. Under the Hill‐Mandel condition, directional orientation averaging was used to map the representative‐element response to the specimen scale, recovering the macroscopic fiber‐contributed shear stress. A parametric suite of three‐dimensional finite‐element analyses was conducted to obtain the interfacial friction coefficient ( μ ) and the elastic‐slip threshold (ES) in the contact law. Parametric analyses of Loess–fiber interface shear across different normal stress levels demonstrate a transition from bond‐controlled resistance to friction‐controlled sliding. Higher normal stress delays the onset of friction‐controlled sliding. The resulting two‐parameter map reveals that μ and ES jointly govern the strength and slip of the interface. Within the tested normal stress range, it delineates a high‐strength plateau for μ of at least 0.40, an effective ES range of 0.0035–0.0045, and an optimal contact‐scale slip range of 0.3–0.6 mm. The study presents an energy‐consistent micro‐to‐macro traction–separation framework for identifying and validating Loess–fiber interface parameters, supporting design quality control and deformation control in reinforced loess.