Scour in bridge piers on non-cohesive fine and coarse soil

Abstract

Estimation of scour in bridge piers is necessary for economic and safe design of bridges. Although a large number of mathematical models are available, scour estimation in Indian bridges is done by empirical equation like Lacey in both fine and coarse soil. Total scour depths in piers, founded on fine soil, are estimated in five bridges in India using different mathematical models and are compared with those found by IRC method based on Lacey’s theory. IRC method is found to overestimate scour in all the cases and the error is found to vary between 5 and 275%. Local scour depths in bridge piers founded on coarse soil are observed at five bridge sites in Mississippi river basin in U.S.A. Scour depths observed are compared with those predicted by different mathematical models and also by IRC method. Compared to IRC method, scour in piers founded on coarse soil, governed both by size and gradation of sediments, is found to be significantly less than that in fine uniform soil under all velocity of flow. It is observed that the scour depths predicted by mathematical models are quite conservative and closer to the observed ones.