Unraveling the Microscopic Mechanics of Kaolinite-Hematite Interfaces in Granite Residual Soil With MD/DFT

SL Li and JS Shen and XY Ma and X Kang and RP Chen, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, 49, 2376-2393 (2025).

DOI: 10.1002/nag.3992

Granite residual soils exhibit exceptional shear strength despite their water sensitivity. This behavior likely results from cemented aggregates, where free iron oxides act as cementing agents for clay minerals. The limitations of traditional experimental techniques hinder direct verification of the hypothesized microscopic stabilization mechanism, which relies on interfacial bonding between free iron oxides and clay minerals. To overcome this challenge, we leverage state-of-the- art molecular dynamics (MD) and density functional theory (DFT) simulations to investigate complex interactions and mechanical characteristics at the interface consisting of kaolinite (001) and hematite (001) surfaces. Simulation results demonstrate that kaolinite (001) and hematite (001) surfaces tend to evolve toward energy minimization, forming a highly stable and adhesive kaolinite (001)-hematite (001) interface through hydrogen bonding and Fe-O ionic bonds. Exceptionally, this interface exhibits dual stick-slip friction behavior due to the misalignment of center atoms in Fe-O and Al-O octahedra and the shear-rebound deformation of hematite. Moreover, the interface frictional force exhibits a linear relationship with the normal load, while the microscopic friction angle and cohesion demonstrate a dependence on sliding velocity, which is in contrast to Amonton's law. This research unveils the microscopic underpinnings of stable aggregate formation in granite residual soil and offers a novel perspective on the intricate interplay between these components, ultimately elucidating the mechanical behavior of these aggregates.

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