Our company’s main service is construction consultancy, and we undertake surveys, investigation, and inspection work using ROVs and drones as a part of our infrastructure inspection and surveying services. In recent years, demands for underwater surveys work using ROVs have been increasing. The equipment used is a BlueRobotics BR2, to which a mechanical sonar (BlueRobotics Ping360) and on imaging sonar (BlueprintSubsea OcullusM750d) are added and outfitted as necessary.
First, a low visibility scour survey of the piers of a dam lake bridge is introduced. The transparency was about 1 m at underwater, and almost nothing could be seen on the camera image. Observations were made using the mechanical sonar. It was attached to the bottom of the ROV so that it could observe the area near the lake bottom.
Next, the breakwater mound damaged by earthquake was surveyed. The sonar was installed horizontally so that the deformation of the cross section could be observed.
Third, port structures damaged by earthquake were surveyed. We installed GPS on the structures on a trial basis in order to obtain location information, even if only while they were above the water surface. It was confirmed that the addition of location information was useful in understanding the situation under the water surface. Currently, we install USBLs for underwater location monitoring.
The fourth survey was conducted after an agricultural canal tunnel was blocked due to a heavy rain disaster. The collapsed section was 650 m long. The collapse was confirmed at 337 m through the tunnel.
Finally, we expected that a screening test for scour could be conducted using an inexpensive imaging sonar. The results of the test in the pool showed that the target geometry could be determined with very high accuracy, and we believe that this would be applicable for the moat scour surveys.
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