Simulation of Sand-Filled Nodular Pile (SFNP) installation process using DEM

The sand-filled nodular pile (SFNP) is an emerging foundation system that features improved bearing capacity in reclamation sites and accelerates consolidation settlement. This study investigates the filling morphology of the gravel introduced by SFNP installation to further elucidate its formation mechanism and explore its effect on the pile behaviors. The discrete element method (DEM) is employed, incorporating the superposition of gaussian distributions (SGDs) method to achieve continuous gradation and fit the actual particle size distribution (PSD) curve. The numerical model is used to investigate the effect of nodular width, nodular spacing and gravel size on the filling effect of the SFNP foundation. According to the observed gravel filling pattern, the filling gravel can be divided into two zones: source zone and filling zone. The gravel between adjacent nodular segments is invaded by the pile-surrounding soil, making the filling morphology close to an inverted cone shape. The results indicate that increasing the nodular segment width and/or reducing the nodular spacing can effectively expand the filling zone and reduce the invasion of soil around the pile. This may be accompanied by soil squeezing effect, which may increase the driving resistance but can eventually improve the soil around the pile. Although increasing the gravel size can effectively increase the filling zone, it is not effective in preventing the invasion of pile-surrounding soil. These findings can provide practical guidance for the application of the SFNP foundation in engineering practice.