Insight into on compression behaviors of clay from a novel discrete element model considering non-contact interparticle forces

An integrated approach that combines a holistic numerical model and experiments is conducted to understand the compression behaviors of clay, which aims to link the microscopic particle interaction to its macroscopic compression behaviors. A novel Discrete Element Method (DEM) approach is implemented in this study that includes a customized interparticle force model considering the non-contact forces between particles (such as the long-range electrostatic repulsion and short-range van der Waals attraction) besides the direct contact force commonly adopted in the regular DEM model. The parameters for non-contact interparticle forces are obtained with the Atomic Force Microscope force measurement on kaolinite particles. The parameters for contact forces between particles, including the contact stiffness, are calibrated by the back analysis of experimentally measured compression curve of kaolinite clay. The unique DEM model is able to holistically predict the responses of kaolinite sample subjected to odometer test conditions under different loading and unloading paths, which allows to determine the compression index, the swell index and the preconsolidation pressure. The results show the compressibility of clay is linked to the changes in its microfabric subjected to increasing magnitudes of loads, which lead to increasing anisotropic fabric orientations, particularly for the load-carrying particles. The number of direct contacts per particle also increases. The particle platyness is found to contribute to the plasticity of soils when subjected to axial loads due to the irrecoverable change of particle fabric orientation, which is related to the swell index. The memorizing effect of clay on its preconsolidation pressure is found to be related to the particle-scale attraction, and an energy well exists between clay minerals due to the Coulomb repulsive force through the electrical double layer. Overall, this study demonstrates that the macroscopically observed engineering properties of clay, i.e., compression index C c , swell index C s and preconsolidation pressure P p , bear rudimental causes from the fabric of particles and the fundamental interparticle forces. The memory of clay is attributed to the particle fabric and the energy well by non-contact interparticle forces.