Long experience in underwater structural inspections
VRT Finland Ltd has performed complex underwater structural inspections since 2010. We were the first to use sonar scanner for vertical structures; previously the sonar scanners were only been used for hydrographic surveys. As the technology developed, we moved from static sonar to mobile multibeam sonar surveys, which made the service suitable for a quick inspection of wide areas.
As the pioneer of underwater structural inspection, we have been involved with creating a handbook for underwater inspections by the Finnish Transport Infrastructure Agency (FTIA). These guidelines replaced the old handbook for underwater inspections performed by diving. Our inspectors are qualified by the Finnish Transport Infrastructure Agency. We follow the guidelines of Quay Inspection Handbook and Channel Structure Inspection Handbook by FTIA. Those handbooks are currently updated, and a new edition is announced to be available in autumn 2019.
Nowadays, we also aid our customers in further utilisation of the survey data. VRT’s online 3D data utilization platform GISGRO was originally developed for 3D reporting but has now various tools for asset life-cycle management. Via GISGRO the client can view the detailed 3D model of the assetread the inspection report, analyze the results, add own remarks, and even send work orders.
Various types of observations on different structures
The observations depend on the used material, which is most often concrete, stone, steel or wood. VRT’s inspections are conducted with a multibeam echosounder from below water, and a mobile laser scanner and a digital camera from above water structures. The point cloud data forms accurate, coherent model of the structures, which is completed by photographs and the field team’s observations.
On concrete structures, the most common observations are cracking and weathering, which are caused by salt corrosion, freezing or collisions. There can also be rust, calcification or vegetation on the concrete. Stone structures can crack or weather or have missing stones or cracks in the masonry.
Different rust damages, bending or corroding can often be found on steel structures, like steel sheet wall or steel piles.
Wooden structures are vulnerable to decay and splitting. Additional structures inspected by VRT are for example ladders, bollards, and fenders, as well as condition of banks and slopes.
The observations are categorized by severity
The guidelines of FTIA categorizes the observations into four categories.
In GISGRO the observations are marked with icons:
Information icon means the observation is irrelevant in terms of the condition of the structure due to its location or low severity. This type of an observation might for example be an object on the seabed or a deeper or a shallower location within the area.
Typically, the majority of observations are located near the fluctuation area and the front side of the quay and are categorized as slight in terms of severity. The slight damages are mostly cosmetic and do not have an effect on the structure’s carrying capacity. Cracks on the surface or minor casting defects on concrete, beginning corrosion on steel and mild rot on timber are examples of slight damages.
Significant damages are for example bigger cracks, wider weathering or spalling, which, however, do not have an effect on the carrying capacity of the structure.
Severe damages, on the contrary, might cause a risk to the structure’s carrying capacity or use. Missing fenders can cause a damage to the mooring vessels and severe cracking impairs the carrying capacity. Erosion under the structure or discharge of a landfill can even cause a collapse. The criticality of the damage and carrying capacity should always be evaluated by a professional structural engineer or a repair planner with drilling samples or such.
If you are interested about the condition of your underwater assets and would like a consultation about the opportunities for using multibeam sonar scanning, leave us a message and we will get back to you!