Pier scour in coarse bed and cohesive materials Research Paper

Pier scour in coarse bed and cohesive materials - Research Paper Example This results to approximately 60 percent of all bridge failures. The societal repercussions that are associated with failures and the costs that are linked to repair are amplified in Alaska, alternate routes of ground transportation between several cities are not in existence. Bridge culvert damages cost a lot to the economy, for example, in 2002 the damage in Kenai Peninsula was estimated at about 19 million dollars. This led to bridge site examination for scour. This paper therefore seeks to discuss the background of scour, its description, the pier scour, and its equation. Scour Scour is a hole that remains behind when sand and rocks, sediments are washed away from the river bottom. Even though scour often occur at any particular time, the scour action is strong especially during flood season. This is because swiftly flowing water has much energy than slowly flowing calm water to lift and wash away sediments from the river bottom. Scour is of a great concern to bridges. This is be cause if rocks or sediment on which bridge is supported or rest is scoured by the river, it is most probably that the bridge could be very unsafe for travel purposes. For example, in 1987 when the Interstate Highway bridge over Schoharie Creek in the state of New York collapsed following a flood, the Federal Highway Administration demanded that each state to specify bridges on the highway over water that are likely to experience problems of scour and to have the bridges with severe scour identified. This knowledge of bridge sites in which there are potential scour problems will enable the States to improve and monitor the bridge conditions ahead of time before they pose danger to travelers. Types of scour There are three main types of scour that affect bridges. The following are the major types of scour that may pose danger to highway bridges over water: Local scour: this occurs when sediments are swept away from around bridge piers and/ or abutments. Piers in this particular case a re the pillars that support bridges, while abutments are the ones supporting the end of the bridge. Flowing water past abutment or pier may scoop holes out in the sediment resulting into scour holes. Contraction scour: this type of scour occurs the sediments are swept away from the sides and bottom of the river. Contraction scour is majorly caused by an increased speed in water flow as it flows through an opening of a bridge which is narrower than the natural channel of the river. Degradation scour: this is a general removal of sand and rocks, sediments from the bottom of the river by the flow of the river. This is often a natural process of sediment removal that lowers the bottom of the river resultantly. In most cases, the process removes large quantities of sediment with time. Pier scour Piers scour is the removal of sediments around the pier. This occurs when rocks and sand in which the bridge rests are removed by flowing water. This is very dangerous to travelers and may cause high magnitude accidents. Adequate definition of potential pier scour at piers is very essential to a proper construction, design, and maintenance of bridges. Designing cost effective and safe bridge depends on accurate estimate of the depth of scour. Thus, underestimating the depth of the scour can place both human life and structures at risk. On the other hand, consistent