“Out of sight, out of mind”

It is easy to forget something that is out of sight, even though it is a very essential part of your everyday work. That certainly goes for underwater assets. They often face the heaviest wear due to the environmental stress and traffic but at the same time the signs keep hidden under murky waters. Checking the condition of underwater assets also seems laborious and pricy as it is formerly done by divers.

There are plenty of reasons to do regular inspections to underwater assets. Not knowing the condition can lead to unexpected breakdown of the asset, which is much more expensive than repairs on time. There are also safety concerns, which is why many countries have guidelines and regulations about inspections. Even though the situation does not lead to a total breakdown, you can lengthen the asset’s life cycle and save money by predictive maintenance.

What kind of damages can be found in structural surveys?

The survey is done by professional land surveying engineers and the inspection is made by a licensed structural engineer. The inspection data consists of 3D point clouds from multibeam sonar and laser scanners added with photographs and surveyors’ observations from the field. It is also possible to combine photogrammetry data to the model. High-quality georeferenced data is a solid starting point for a thorough inspection.

The usual observations depend on the material of the structure. On concrete there can be weathering or cracking, steel sheet walls can wave or bend. Because the inspection includes also the topography of the seabed near the structures; erosion, scouring, and possible empty space under the structure can also be detected. Scouring near vertical structures is something usually missed in diver inspections, because the diver needs to be really close to the structure to detect damages there. Small leaks of the filling material from steel sheet walls can escalate surprisingly soon and even cause the quay to collapse. We categorize the findings into four categories in terms of damage: Information, Slight, Significant, and Severe. That helps the prioritization of repairs.

The marine and underwater structures can be of different ages, and especially in Central Europe and the UK the age of the structure can already be hundreds of years. That naturally also means more damages, but even on new structures there can be significant observations. Sometimes we find objects on the seabed which have been left there in the recent construction phase and can be a threat to port traffic.

How can you use the survey results?

Multibeam sonar survey is an efficient tool for every phase of an asset’s life cycle. The results can be used in planning the new construction, inspecting the condition of existing structures or planning and verifying the quality of repair projects.

Knowing exactly the conditions of an underwater construction site makes sure that there are no surprises causing delays to the project. It is also good to check the site and structure after the construction project to have an as-built model for future use and confirm that there are no objects or materials left from the construction.

Information about the existing structures is essential for maintenance purposes. If the structure is older, there might not be up-to-date drawings available. Georeferenced 3D data is a great starting point for storing details of a structure and its maintenance procedures. Observations about the structure’s condition aid the decision making in maintenance and repeated surveys give a possibility to compare data and evaluate if the damage is progressing. It is much easier to allocate the resources to maintenance when you have the accurate information about the condition of the structure.

Professional interpretation of the survey data and easy online reporting makes the difference

Survey equipment has become more affordable and many companies and asset owners already have the capability to perform sonar surveys. Many of the surveyors have concentrated on one smaller section of the field of surveying, though. VRT is a pioneer in 3D structural surveys and we have the know-how for the whole process in-house. The project flows easily from the client’s point-of-view, when everything from planning the survey areas to delivering the data with categorized observations is run by one team. This confirms that the client’s time and money is well spent and top quality 3D data is put to work for more efficient and safe asset maintenance.


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Karri Kolehmainen & Ville Mäkeläinen

Karri Koistinen

+358 40 0604927

karri@vrt.fi

 

 

Ville Mäkeläinen

+358 44 513 2222

ville@vrt.fi

 

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