Bridge Scour Monitoring Using Ultra-Sonic Sensing Technology

Scour is the process of the erosion of foundation materials below bridge piers and abutments during floods and rapid river flow, resulting in lower elevation river or change of river course. It is one of the major causes of bridge failures. Each year many bridges failed due to scouring during flood. Scour is one of the major causes of bridge failures. Scour depth is the most critical factor for bridge safety against scour, the mon-itoring of scour depth is essential. Up to now there have been many ways to monitor the scour depth at bridge piers, yet many shortcomings abound still. In order to overcome the shortcomings in existing methods, a bridge scour monitoring system based on the principle of ultrasonic sensing is developed and tested through experiments simulating the scouring process around bridge pier. The main research contents are as follows.The monitoring system is designed using ultrasonic sensing technology based on the favorable characteristics ultrasonic sound. Ultrasound has a good transmitting per-formance with very good direction and can be reflected at the interface of two media with different acoustic impedance. The system works by placing the ultrasonic probe in a tube which enables the probe to move upward and downward. The ultrasonic pulse will be reflected at the water-sediment boundary. When ultrasonic probe is within the depth of the scour, there is a reflected signal. The point the scour depth has reach can be determined from the waveform and the depth of scour can obtained by measuring the displacement of the transducer.The monitoring system is tested trough experiments simulating the scouring process around bridge pier. The scour process is simulated by making water plowing pass the pier model and monitored using the proposed system. Later the deposition process is simulated and monitored, too. The experimental study has showed that the proposed system can monitor the scour process at real time. The contour of the scour hole can be obtained using experimental data.Four typical failure modes of bridge failure caused by scour are analyzed. Their ultimate state conditions are also given. Then two types of bridge scour protection me-thods and their characteristics are introduced. Finally a brief principle of choosing a bridge scour protection method is provided which may be instructive for safety access- ment and protection of bridge structures against scour.