3D DEM simulation of plain and rotary axial jacking of piles

Increasingly stringent environmental regulations on underwater noise have led to the development of silent piling methods for offshore wind turbine foundations, such as plain axial jacking. However, the reaction force required for plain jacking equals the piles axial compressive resistance, which may exceed the capabilities of offshore vessels. Rotary jacking, which involves pushing and rotating the piles, reduces the axial reaction force by rotating the shear stresses along the pile shaft and reducing pile plugging for open-ended piles. Despite its potential, the effects of rotary jacking on pile plugging are not well understood, hindering its development as an alternative to traditional pile driving. The discrete element method (DEM) simulates granular materials as assemblies of rigid particles, allowing for the simulation of large deformations during pile jacking. DEM also provides insights into the physical mechanisms within the ground, informing physical tests and guiding prediction methods. In this numerical study, an open-ended pile was subjected to both plain axial and rotary jacking in a polydisperse sample with upscaled particle diameters to reduce computational costs. Results indicated that rotary jacking reduced the necessary reaction force by 60%, due to (1) the rotation of the shear stress mobilised along the interface and (2) the reduction of pile plugging due to the disturbance created by the pile rotation. The coefficient of lateral earth pressure and the stress within the pile plug could be calculated and compared with the existing literature. These findings have significant implications for predicting the installation resistance and in-service capacity of rotary jacked piles.