Effects of pier inclination angle and direction on local scour at rectangular and circular piers

Abstract

The understanding of scouring around piers is crucial for ensuring the safety of bridges. However, the effects of bridge pier inclination angle and pier inclination direction on river bed topography have not been extensively explored. In this article, the effects of pier inclination angle and direction on local scouring were experimentally studied for both rectangular and circular bridge piers. Three pier inclination directions (upstream, downstream, and laterally inclined) were investigated, along with various pier inclination angles and flow intensities. Eighty-seven experiments were conducted on a uniform sand bed. It was observed that the relative scour depth was highest for upstream-inclined piers and lowest for downstream-inclined ones, with intermediate values for vertically and laterally inclined piers. Moreover, the scour depth decreased significantly for downstream-inclined piers with increasing pier inclination angle, while it increased for upstream-inclined piers. The relative scour depth increased with higher flow intensity, ranging from 1.2 to 3.7 for rectangular piers and 1.3 to 2.45 for circular piers. Approximately 72.5%, 74.5%, 72%, and 75% of the equilibrium scour depth were reached after about 10% of the experimental duration for flow intensities of V/Vc = 0.75, 0.85, 0.95, and 0.98, respectively. Rectangular piers exhibited higher scour depths compared to circular piers. Furthermore, relative scour depths for downstream-inclined rectangular and circular piers were reduced by approximately 34% and 15%, respectively, relative to vertical piers, while for upstream-inclined piers, they increased by about 9% and 7.5%, respectively. The corresponding reductions for laterally inclined rectangular and circular piers were 4% and 3%, respectively. Several available predictive equations for scour depth were compared, and the one that correlated best with the data was introduced. Additionally, new equations were developed to predict maximum scour depth, considering pier inclination angle and direction, which showed good agreement with previous data.