A Mesoscale Perspective on Micron-sized Clay Aggregates Compression: Insight from Coarse-Grained Molecular Dynamics

In this paper, coarse-grained molecular dynamics (CGMD) employing the Gay-Berne (GB) potential was applied to investigate the mesoscale compression behavior of micron-sized clay aggregates fulfilled with explict pore water fluids. A systematic set of CGMD-compatible methods was proposed to characterize the mesoscale structure of clay. Simulation results revealed a topology transformation from loose “honeycomb” structure, featuring homogeneous clay platelets orientations, diverse pore morphologies, and normally distributed pore size, into dense “band type” structure, characterized by uniform clay platelet orientation, flattened pore morphology, and micron-sized pores. The pore water migration showed a three-stage progression. Initially, pore water fluids fully or partially filled the clay pores of various shapes. Subsequently, pores flattend gradually while pore water molecules adhered onto clay platelets. Finally, clay platelets “lay down” to form a flat micropore full of water. Meanwhile, the clay skeleton transitioned from stability to collapse and ultimately to failure with the increase in pore pressure heterogeneity. With axial strain increasing, the clay aggregates initially experienced elastic deformation, followed by plastic deformation and lattice fracture. These findings suggest that the microscopic failure mechanism of clayey soils under external stress involves the development of heterogeneous microstructural alterations and non-uniform pore water pressure gradients. In conclusion, this research offers novel insights into the micro-mechanisms controlling the macroscale compression behaviors of clayey soils and highlights CGMD technique as a powerful tool for investigating microscopic response of clay under different conditions, including high geostress, high hydrostatic pressure, freeze–thaw cycles, and cyclic loading–unloading.