Open ended steel pipe piles (e.g. large diameter monopiles) installed by impact driving are the common foundation technique for offshore wind turbines (OWT). At several stages of the lifetime of such piles, different measurements may be taken at the pile. To determine the load bearing capacity, pile driving monitoring is carried out during installation. For the investigation of long term behavior, condition monitoring systems are installed. Other aspects, such as underwater noise emissions, may require different kinds of measurements at the pile.
Due to the cyclic loading of the piles for a period of about 25 years, fatigue is an important factor in the pile design. Therefore, encroachments into the steel structure like welding or drilling lead to high efforts in the certification process and should be avoided after the pile design is finished. Especially for measuring campaigns, which have not been part of a project at an early stage, alternative installation methods are required.
Within a research project to investigate the noise emissions during impact driving of monopile foundations, the authors have realized an autarkic pile driving monitoring with strain measurements and acceleration measurements in different measuring sections above and below the mudline. Sensors, cables, protective profiles and the data acquisition unit have been installed without drilling or welding. In later projects, components for a conventional pile driving monitoring and measuring equipment for condition monitoring systems have been installed at monopiles of different offshore wind farms (OWF).
In the paper, the necessities for bonding different components as well as their technical solutions will be shown. Heavy equipment exposed to high accelerations during pile driving requires elastic damping. Sensors have to be attached rigidly to the pile and need a sealing to avoid intrusion of water. Protective profiles below the mudline have to withstand abrasion and high shear stresses. Results of laboratory tests as well as measurements during pile driving are presented.