Monitoring Technique for Local Scour around Bridge Pier

Local Scour is one of the key challenges for construction of bridge in deep water, especially, for bridge at the estuary of Yangtze River. The flow condition here is really complex due to rugged topography and evident tide influence. Local scour might deteriorate for the disturbance during construction of pile group and bearing platform. Thus, stability of riverbed becomes the most fundamental for the safety of pier foundation, including construction of temporary construction platform and installation of pile group. So, protection of riverbed soil is usually started before foundation of bridge. To study the real result, multi-beam echo sounder using ultrasonic is often adopted to periodically measure and mapping riverbed topography. But due to the effect of foundation, blind area often exists around the pier. At Sutong Bridge, vibrating wire piezometers using to continually monitoring local scour happened within and around pile group. Multi-beam Echo Sounder is using for the large-scale detection progress during and after construction, and the vibrating wire piezometers is using for the small-scale detection within and around the pier foundation soil. Special protection applied for the vibrating wire piezometers and its cable to avoid harm from torrent. The result shows: 1) Different scale detection systems, using vibrating wire piezometers and multi-beam echo sounder separately, can get enough and better information for the monitoring of local scour occur around pier. As an example, monitoring of riverbed protection at Sutong Bridge lead out the conclusion that protection does effect on riverbed and weaken the scour around pile group. 2) Special protection for the Vibrating Wire Piezometers and its cable is really needed.