Genesis and evolution of metastable internal support structures in loess: Pore-scale insights from microfluidic seepage experiments
Description
Loess microstructural genesis and evolutionary mechanisms are of critical significance for elucidating its distinctive water sensitivity and metastable behavior. Building upon the fundamental classification of overhead and interlocking structures, this study identifies and defines a critical intermediate fabric: the “Metastable Internal Support Structure”. We reveal that this fabric originates at the inter-granular throat contact zones within the silt-dominated skeletal framework. The structure exhibits significant vertical differentiation, evolving from discrete, scattered forms in shallow layers to continuous, interconnected networks in deeper strata. Mechanistically, the genesis of this structure is driven by evaporation-induced capillary forces. Initially, fine particles adhere to the skeletal surface to form a “particle coating,” serving as a precursor that reduces pore throat distance. As evaporation proceeds, particles undergo directional aggregation along the retreating menisci of liquid bridges. We demonstrate that the resulting morphology is strictly controlled by the fine particle concentration within these bridges. Under high-concentration conditions, particles exhibit anisotropic alignment along the bridge's principal axis, forming robust “liquid bridge-shaped supports” that maintain structural continuity. Conversely, low particle concentration leads to rapid collapse following liquid bridge rupture, manifesting as “necking-type” local clogging rather than stable support. Functionally, these microscopic supports play a dual role: they reduce hydraulic conductivity by segmenting pore and provide lateral constraints to the skeleton. However, these cemented flocculated components are highly susceptible to disintegration upon re-wetting, leading to rapid structural collapse. This research elucidates the formation mechanisms of loess microstructure and the causes of its vertical differentiation, providing a novel micromechanical basis for understanding the vertical variability in soil stability and its implications for landform evolution.
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Institutions
- Shandong University of Science and Technology