Zhu, R.-H.; Zheng, J.-H; Zhang, J.-B.; Wang, H.-K.; Li, T.-F., and Liu, R.-L, 2020. Application of the sonar detection technique to inspection of vertical quay wall. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 325-329. Coconut Creek (Florida), ISSN 0749-0208.
The sonar detection technique can play an important role in underwater inspections to the port and coastal engineering, and such inspections may prevent or mitigate disasters from the coast engineering. This technique has been widely used in underwater surveys, but little research has been done on the inspection ability for vertical quay walls. The sonar detection of vertical quay wall has its own characteristics, and the theoretical resolution can be calculated from the formula. However, affected by the working conditions and environment, the inspection ability is not the same as the theoretical result. This study introduced and performed underwater field model experiment to study the actual inspection ability of the vertical quay wall with a homemade vertical structure concrete model, and conducted the experiment in harbor water at different working distances. The 3D scanning sonar with 1 degree transmitting beam angle was tested to be valid to gather data at the proper working distance to study the detailed inspection of vertical targets with sizes no less than 5 cm, and the sonar is able to distinguish long strip-shape targets as a whole with width no less than 1cm at working distance of no more than 1.5m. Results of the field inspection for the caisson joints of a gravity wharf by different sonars were compared with each other and verified by underwater video shootings. The 3D scanning sonar was verified to be valid in the caisson joint inspection, and MBES was tested to be fast in working efficiency but with errors caused by long working distance, which was restricted by the sea conditions.