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Monitoring system takes the uncertainty out of Gravity Based Foundations settlement

WHAT ARE GBFS AND THEIR CHALLENGES?

Gravity Based Foundations (GBFs) or Gravity Based Structures (GBS) are a foundation type that originates in oil and gas production facilities in the North Sea. The structure relies on its own weight and the capability of the seabed to withstand the vertical load of that weight, in order to remain stable. GBFs have been used sporadically in offshore wind while monopile and jacket foundations dominate the market.

There is potential that GBFs could be used on more projects in the future as the economics of these structures could prove more financially interesting than other solutions on some of the newer sites where the soil has high bearing capacity.

One of the areas that need to be looked at when installing and operating these large concrete blocks is the settlement behaviour of the structure due to probable compaction of the soil under the weight of the GBF. This is monitored pre- and post-solid ballasting.

Pulse, a structural monitoring brand in Acteon’s Data and Robotics division, has developed a system for providing accurate and robust online monitoring of the GBF attitude during the settlement phase.

Gravity Based Structures

HOW TO MEASURE GBF SETTLEMENT BEHAVIOR

Pulse’s system uses survey precision DGNSS receivers and high-precision inclinometers to measure GBF settlement behaviors. The system is aligned and calibrated with in-field topographical measurements of the structure provided by UTEC, a geo-services brand in Acteon’s Data and Robotics Division. Measurement data is then fed back to shore for data processing. The system uses a variety of communications networks offshore for data transmission, adding to the flexibility of the system. As a result, the client’s engineering team can see up-to-date settlement measurements for the whole field on a web portal dashboard screen. This gives the asset owner a reliable and insightful view of the GBF behaviour and potential intervention requirements.

Pulse is currently offering this system to developers and installers on global GBF projects. Brian Taylor, sales director at Pulse says “There is an increasing need for this type of monitoring system, particularly in large concrete GBFs used in wind farms. This versatile system can also be adapted to monitor the suction cans for suction bucket foundation structures and any other structure which is settled into position offshore.”

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Structural health monitoring; visualising asset condition and providing remediation and life extension solutions.

Acteon’s asset integrity and monitoring solutions are designed to help our clients carry out diagnostic and remediation work including further monitoring/deep dive and the provision of proprietary retrofit cathodic protection CP packages suitable across a wide range of applications in marine energy and marine infrastructure markets.

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