Major failure of structures usually occurs during flood flows due to scourin, sinking and sliding. These types of failure are considered to be in close relation to the dynamic behavior of bed material around the structures. Failure of bridges due to the phenomenon of scouring around piers is a common, natural problem of river hydraulics. Experiments were carried out to investigate the characteristics of pore water pressure and effective stresses in the bed material around a circular bridge pier under abrupt change of water pressure. A laboratory model was used to clarify the effect of the variation of water pressure to determine the mechanism of the collapse of circular bridge pier during flood or storm waves. The experimental results showed that the bed material under suddeen change in drop of water pressure near the pier was weakenend by an increase in excess pore pressure, followed by a considerable quick removal of bed material.
Abrupt water pressure change