PSI - Issue 20

A.A. Antonov et al. / Procedia Structural Integrity 20 (2019) 270–277 A.A. Antonov et al. / Structural Integrity Procedia 00 (2019) 000–000

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the image quality, but at the same time, the sounding rate slows down. The value of the dielectric capacity ε is assumed constant at inspections in freshwater bodies. In the profile recording mode, “continuous” recording of lines into a profile is performed as they are detected at regular intervals of time. Therefore, the georadar was moved as evenly as possible so that no compression or tension sections appeared on the profile. The survey is areal. The width of the main channel part is ~ 1775 m according to the project. Profiles located across the trench are recorded every 70-120 m, their length is ~ 300-400 m. Four profiles are located along the trench 60 and 120 m upstream and downstream. Their length is ~ 1800 m. The Hydra-500E side-scan sonar installed on the boat was used for the inspection of the river bottom as well (Fig. 1b). For the inspection of the bottom of the water area, the antennas demonstrated in the figure are rotated 180 ° and lowered into the water to a fixed depth of 30 cm. As a result of sending sounding signals and receiving echoed signals reflected from the bottom, an acoustic image (a photo) of the bottom, as well as the echo-sounder readings, are formed on the monitor (portable PC) of the system in the form of two bands along the course of the vessel (one on the left side, the other on the right). The RD-8000 line locator was used to determine the planned-high-altitude position of two lines in the floodplain section of the underwater gas pipeline (Fig.2a). The locator detected the position of the pipeline axis for setting the control point. The control point is fixed with a surveying rod on the ground and numbered. After fixing all the control points in the area, the line locator was installed at the control points alternately and the depth of the pipeline axis was measured. At each control point, the depth was measured at least three times. An electronic tacheometer was used to determine the planned-high-altitude position of the control points (Fig.2b). The tacheometer, which is centered, leveled and oriented towards the adjacent temporary control station, was installed on one of the permanent control stations. To determine the tacheometer's height, the height of the device to the center of the station was measured with a tape measure. The accuracy of centering the device in terms of the benchmark center is 1 mm.

Fig. 1. a) OKO-2 GPR; b) Hydra-500E SSS mounted on a rubber boat in transit position.

Fig. 2. a) RD-8000 line locator; b) electronic tacheometer.