Diagnostic methods of quay wall with acoustic measurement systems

We used two acoustic measurement systems to assess the state of a quay wall. Collapse and subsidence of quay walls at harbors are often reported, and the development of a diagnostic method to help prevent collapse has become a significant concern. Collapse normally occurs because of an air hole inside the quay wall. Therefore, a robust, accurate diagnostic system to detect air holes is required. Hence, we evaluated a new diagnostic system that can assess the inside and outside states of an underwater quay wall. In this study, two acoustic measurement systems are utilized: dual-frequency identification sonar (DIDSON) and a narrow-beam parametric sub-bottom profiler (SES2000). The field experiment was performed at Iwanai port in Hokkaido, Japan (42° 59´ N, 140° 30´ E) on a damaged quay wall. DIDSON raw data was used to generate an image mosaic and a three-dimensional image of the quay wall surface. SES2000 created an acoustic profile of the inside of the quay wall. External and internal acoustic images of the damaged quay wall were reconstructed by data collected by DIDSON and SES2000. We detected a corrosion hole and age deterioration at some survey points using two- and three-dimensional images. The state of the quay wall was quantified and compared with the results obtained from direct underwater measurements by a diver.