Large deformation numerical assessment of rock anchor response under axial loading for offshore renewable energy applications

The study presented in this paper aims to advance the current understanding of Rock Anchor (RA) performance under axial loading through large deformation numerical analyses. Simulations are conducted using the Geotechnical Particle Finite Element Method within a coupled hydro-mechanical framework. Experimental data from the literature is used to calibrate a strain hardening plasticity constitutive model for rocks. The calibrated model is then used to investigate rate effects on the axial response of a novel rock anchor design. The axial pullout induces rock dilatation at the bottom edge of the anchor with the consequent formation of a zone of negative water pressure change and a bulb of positive pore water pressure change above it. Depending on the pullout rate, distinct drained, partially drained, and undrained hydraulic regimes are identified. These, along with the variable damage distributions, are shown to influence the rock anchor axial capacity considerably. The geometrical and elastic properties of the rock anchor modelled as a deformable body, along with the interface friction angle between the anchor and the rock are also explored. Results such as load capacity curves, stress path evolutions, and stress distributions on the rock-rock anchor interface are analysed emphasizing their impact on rock anchor design.