Investigating Effects of Particle Scaling for Cavity Expansion Simulation Using Discrete Element Method

Abstract

The Discrete Element Method (DEM) has been widely adopted in investigating many complex geotechnical related problems due to its capabilities of incorporating the discontinuous nature of granular materials. DEM can be very effective when simulating soil encountering large deformation or distortion (e.g. cavity expansion) since other numerical solutions may experience convergence problems. Cavity expansion theory has widespread applications in geotechnical engineering, particularly in problems concerning in-situ testing, pile installation, underground excavation, deep foundations, to name a few, explaining why cavity expansion simulation using DEM is worthy to be conducted. Although many discrete element numerical studies have been carried out to investigate the problems associated with granular materials, there are very limited findings reported regarding the effects of particle size scaling. Therefore, in this study, a series of three-dimensional numerical models with different size scaling factors have been developed using PFC3D software, developed based on DEM. It should be noted that the numerical model has been calibrated for medium sandy soil adopting the experimental results obtained from the triaxial test in drained condition. To examine the effects of particle-scaling during cavity expansion, several cylindrical cavities were created and expanded gradually from an initial radius to a final radius, while stress variations, volumetric changes, as well as radial movements of gauge particles were monitored during the entire simulation. Furthermore, the internal cavity was loaded using a constant strain rate, while the outer boundary was automatically controlled through a servo mechanism to maintain a constant external pressure adopting appropriate subroutines. Cavity pressure variations, stress-strain responses and radial displacement of gauge particles obtained from different simulations were discussed and compared. It is observed that the particle scaling factor beyond a certain limit can affect the soil response during cavity expansion.