DEM analyses of oedometer and wetting tests on unsaturated structured loess

To investigate the macroscopic and microscopic mechanical performances of unsaturated structured loess, three-dimensional discrete element analyses of oedometer and wetting tests on the unsaturated remolded and structured loess are performed. Firstly, interparticle adhesive force is incorporated to consider the effect of van der Waals attractions and capillary forces, and bonds are introduced in the 3D contact model to calculate the influence of chemical bond. Then a loose and homogeneous DEM sample is produced by the multi-layer under-compaction method (UCM) and the installation of van der Waals forces. The capillary forces and bonds are installed to the contacts to simulate the unsaturated and structural properties, respectively. After parameter determination, stepwise loads are applied and then the sample is wetted at different vertical loads. The simulation reproduces the main mechanical behavior of oedometer and wetting tests on structured loess. Concerning the bond breakage, there is a threshold of vertical stress in the oedometer tests. The bond breakage number of the sample subjected to loading-wetting is similar to the number of the sample under wetting-loading sequence. The wetting-induced volumetric strain is affected by the bond breakage.