Monitoring Monopile Penetration Through Magnetic Stray Field Measurements

Abstract

Current methods to infer the penetration of a steel monopile during an offshore installation are rather inaccurate. Since a large number of foundation piles will be installed offshore in the coming years, a reliable technique to infer the penetration depth is vital. This paper proposes a non-contact method to monitor the pile progression into the seabed based on measurements of the magnetic stray field that permeates the air surrounding the structure, eliminating the necessity of a predefined pattern on the pile's surface. A simple magnetisation model for the monopile is proposed from which the relative motion between the moving pile and a stationary magnetic field sensor can be extracted. Comparison between the measured and simulated stray field data show a promising correlation, providing the basis for the new non-contact monitoring technique that is applicable offshore.