Monitoring of Scour Around Bridge Piers and Abutments
Scour of the riverbeds around bridge supports is the most frequent cause of their failures. Maintenance and repair costs of the bridges damaged by scour effects are significant, but it is estimated that the social costs are five times higher than the direct repair and replacement costs. The bridge supports are subjected to the scour effects due to the erosive action of the flowing water, involving soil loosening from the bottom and the banks of the watercourse. The condition for the proper monitoring of scour is to understand its nature. The knowledge of the phenomena occurring during the high water flow in the area of the bridge supports is crucial to properly assess the current condition and to develop proper maintenance actions. Scour may be the consequence of: narrowing the watercourse a natural or man made, including construction of a bridge, lateral movement or lowering of the stream bed, hydraulic works shortening the length of the meandering section of the watercourse, changes occurring in the catchment area of the watercourse, other changes in watercourse hydrology. Construction of a bridge in the certain area disturbs natural stream flow conditions, especially the flood water and may change the terms of the normal water flow. The presence of a bridge causes the stream flow cross section reduction, which increases the speed and intensity of erosion of the streambed. River tends to stabilize its bed in order to restore the natural flow section. Bridge supports also change the laminar water flow and turbulent flow. Scour present around a bridge supports can be monitored by the mobile and fixed devices. Portable scour monitoring devices are mainly: different types of probes such as: sticks, tape or rope with weights and bars used by divers and sonar acoustic measuring devices. Stationary equipment is used for continuous or regular scour monitoring of the bridge supports of the bridge, for example once a day, once a week. They are stationary devices including various types of robotic probes and stationary hydroacoustic measurement systems. Stationary device can be installed on a support or near the bridge, usually at the head of the pillar, or in the ground near the bottom of the watercourse. It should be installed near the site of the anticipated greatest scour. The device interacts with the data logger, which can be read on the site or transmitted to a remote control unit. The article presents the principles of scour monitoring near the bridge supports, developed during the project "Monitoring system for bridge supports and their surrounding areas" co founded by the Polish National Centre for Research and Development under the program Innotech. During the project monitoring system for bridge supports was developed with specialized software for online data visualization. The article presents selected measurement results from the sonar measurements.