A case study on pier scour monitoring at Incheon Bridge in Korea

The local scour is a critical factor of the bridge stability. Scour depths are usually determined using empirical formulas or numerical studies or physical model tests in more complex cases. But all methods to estimate scour depths always include uncertainties resulting from hydraulic and geology conditions, therefore it is necessary to overcome these by in-situ monitoring for real bridge scour. In this study, the local scour depths were evaluated at a important pier of Incheon Bridge. Generally, local scour is closely related to bottom characteristic and bottom shear stress. If tidal current is strong and ground condition is soft, bottom shear stress is high so the possibility of local scour occurrence is increasing. As the result of bottom shear stress evaluation, W1 pier of cable-stayed bridge section is selected for scour monitoring. Two monitoring methods are applied. One is a periodic scour survey using a boat. The other is a installation of the profiling scour monitoring system which was newly developed, attaching a profiling scan sonar for this study. The measurements of the new system are compared to measurements of the survey using a boat. The results indicate that the survey using a boat is effective in evaluating the maximum scour depth and the profiling scour monitoring using a new system would be more cost- effective than the previous scour monitoring system if the pier foundation consist of many piles with large diameter.