The compressibility of kaolin clay: a micromechanical perspective based on DEM

The mechanisms governing the compressibility of kaolin clays are investigated through discrete element method simulations of oedometer tests, where clay platelets are modelled as clumps of spheres. A contact model incorporating the long-range van der Waals (VDW) attraction and electrical double layer (EDL) repulsion, alongside mechanical forces, is formulated to reproduce interplatelet physicochemical forces in agreement with the DLVO theory. Oedometer simulations are conducted on assemblies of platelet particles with varying aspect ratios. The significance of different interparticle forces is evaluated by partitioning the total stress into different contributions, revealing that while the EDL interaction is negligible for practical stress levels, the VDW interaction induces tensile stresses comparable to mechanical forces at compression stresses up to 15–70 kPa. As compression stress increases, the significance of the physicochemical interactions decreases, while mechanical contact forces become increasingly dominant. Additionally, increasing the VDW force or decreasing the EDL force leads to increased stress from mechanical contact forces, consistent with the modified effective stress concept. After sedimentation, the clay platelets initially form an open-flocculated structure with edge-to-face association dominating the fabric. Upon compression, the platelets tend to rotate their normal vectors towards the compression direction and aggregate into a face-to-face arrangement.