DEM Investigation of Energy Dissipation at Particle Contacts in Granular Soil Under Cyclic Torsional Shear

Damping is an important dynamic soil property that has been well-studied on the continuum scale. However, particle-particle interactions that are responsible for damping in dry soil are relatively less studied due to the difficulties in accessing energy loss at particle contacts. This study attempts to evaluate contact energy dissipation numerically on the particle scale. A model based on the discrete element method (DEM) was first developed and validated to simulate the cyclic torsional shear test. A parametric study was then carried out to study the distribution of contact energy dissipation inside the soil specimen. The effects of shear strain level, confining pressure, and specimen void ratio were investigated. The results show that, as shear strain increases, contact sliding and energy dissipation first occur in the weak-force network and propagate towards the strong-force network. At the same shear strain level, an increase in confining pressure results in a decrease in the number of sliding contacts and a higher energy loss per contact. At the same confining pressure and shear strain level, an increase in specimen void ratio results in less total energy loss and a smaller percentage of sliding contacts in the specimen. It is also found that particle contacts at the top one-third of the specimen have a higher tendency to slide and higher energy loss per contact and, therefore, contribute to the majority of the total energy loss in the specimen.