Simulation of pile installation in chalk: Discrete and continuum approaches

Chalk is a type of porous rock formed from cemented calcite grains. It is widely found in areas across the UK, and is present beneath the North Sea where offshore wind turbines are being installed. Large piles are often driven into chalk to support these turbines. However, the installation process can cause the intact rock below the pile to crush, creating a putty-like material with different mechanical properties from the original rock. This unpredictability has made it difficult to design piles that are appropriate for use in chalk. This paper presents two approaches to modelling open-ended pile installation in chalk. The first approach is based on the Discrete Element Method (DEM), which represents the rock as separate particles bonded together. A new contact model is proposed for highly porous rocks. The second approach uses the Geotechnical Particle Finite Element Method (GPFEM), which has been adapted to account for the large displacements and nonlinearities of the problem. With GPFEM the coupled hydromechanical effects developing during pile installation are investigated using a robust and mesh independent implementation of an elasto-plastic constitutive model at large strains. With DEM the micromechanical features of pile plugging are explored and the mechanisms behind radial stress distributions inside and outside the plug are unveiled. Although both approaches have their challenges, they have been successful in modelling pile installation experiments at model scale. This offers the potential for a closer examination and improved understanding of the mechanisms underlying open-ended pile installation in chalk