Development of a novel rock anchoring system for floating offshore renewable energy mooring

Abstract

The rapid expansion of offshore renewable energy and the deployment of floating systems in deep waters are driving the necessity for reliable and efficient anchoring solutions capable of operating under strong wind and tidal actions. The industrial partner, Schottel Marine Technologies, developed a novel self-drilling Rock Anchor designed for fast installation in various rocky seabeds, both in shallow and deep waters. However, current knowledge of rock failure mechanisms and rock–anchor interaction behaviour for such innovative systems is limited and requires advanced investigation. Furthermore, current design practices for rock anchors have remained largely unchanged over recent decades, relying on conservative methodologies that often lead to over-designed and costly solutions.

This thesis employs a combined experimental and numerical approach to develop robust design methods that can be adopted by industry to optimise current anchor configurations. The research addresses this gap by proposing a specific design methodology for groutless anchoring solutions.

A state-of-the-art review of classical and innovative anchor systems is presented, along with previous field and numerical studies. The literature review critically examines the assumptions, strengths, and limitations of traditional analytical design methods under axial and lateral loading conditions.

Large-strain numerical analyses were carried out using the Geotechnical Particle Finite Element Method (GPFEM) to enhance understanding of Rock Anchor performance under static axial and lateral loads. An advanced constitutive model for rock implemented was used to evaluate the influence of key anchor parameters on load capacity, providing insight into failure mechanism propagation, stress distribution at the rock–anchor interface, and rate effects. The results highlight the formation of both deep and shallow failure mechanisms, depending on anchor embedment depth. Increasing finger inclination and interface friction angle was found to enhance load capacity. The numerical method effectively captured shear localisation in weak rock and realistically represented failure in intact rock.

The experimental programme included small-scale and field tests investigating the anchor’s response under multi-directional loading representative of offshore conditions. A bespoke tilting frame was designed for testing undercut anchors in weak and hard rock under inclined loads. Observations revealed classical pull-out and wedge failure modes, as well as the influence of load angle on pre-tension loss. Contrary to expectations, no rock damage or cracking was observed during installation in weak rock and concrete.

A field test campaign in Dörth (Germany) provided geotechnical characterisation, anchor performance data, and validation for a 3D GPFEM model, which supported the development of a new Limit Equilibrium method. Extensive parametric analyses using 2D GPFEM produced industry-relevant p–y and t–z curves. The outcomes offer a practical design tool for the additional development of this anchoring technology.

This work contributes new tools for the offshore industry and advances the understanding of anchor–rock interaction behaviour under realistic static loading conditions.

Date of Award	2025
Original language	English
Awarding Institution	University of Dundee
Supervisor	Matteo Ciantia (Supervisor), Michael Brown (Supervisor), Ana Ivanovic (Supervisor) & Nick Cresswell (Supervisor)