Scour around Bridge Pier under Abrupt Change of Water Pressure

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A substantial damage of a number of bridges has been reported so far especially during flood flows or storm waves. During these natural conditions, the abrupt change of water pressure variation occurs near the structures, and it causes failure due to scouring. Considering such a real occurrence in the hydraulic engineering field, this report mainly deals with the experimental results on the distribution of pore water pressure, effective stresses and local scour development around a circular bridge pier carried out in a laboratory channel under abrupt water pressure variation. The results show that the sediment bed is liquefied by an increase of excess pore water pressure under sudden water pressure variation and the equilibrium local sour increases considerably than that of clear-water steady flow at the bridge pier.Further investigations on the wave-induced dynamic behavior of bed material and local scour around a circular bridge pier were carrying out. Under persistent action by water waves, not only the scour of the bed material but also the dynamic stability of the bed material around the bridge pier is a significant reason of bridge failure. Observations were carrying out on the excess pore water pressure, local scour and velocity distributions under clear-water steady flow as well as wave flow around a circular bridge pier using a laboratory flume. The results show that the larger the wave height is, the larger the scour depth becomes. In the case of higher wave height, the decrease of the effective stress was recognized as the increase of the excess pore water pressure. In such conditions, the bed material around bridge pier is removed easily.