Arabian Journal for Science and Engineering https://doi.org/10.1007/s13369-018-3418-5 RESEARCH ARTICLE - CIVIL ENGINEERING Impact of Upstream Bridge Pier on the Scouring Around Adjacent Downstream Bridge Pier Rajib Das 1 · Subhasish Das 1 · Hasanur Jaman 1 · Asis Mazumdar 1 Received: 19 October 2017 / Accepted: 26 June 2018 © King Fahd University of Petroleum & Minerals 2018 Abstract The study aspires to investigate a relative scour condition around three-pier group. It identifies the upstream downstream scour geometries when two tandem piers are placed inline and third pier is placed eccentrically in middle of tandem piers. Laboratory scale experiments were physically performed by gradually varying the intermediate longitudinal spacing in between tandem piers. After each experimental run, the scour formation around the pier group and the dune formation downstream of the pier group are investigated. The main aim here is to experimentally identify and highlight the nature and location of scour formed around and also to identify the location of the dune formed downstream of this pier group due to combined interference of flow. The spacing between the inline piers were varied to identify which relative spacing produces the maximum scour. A detailed investigation shows significant effect of inline pier spacing on scour parameters. It was observed that for such three pier combinations, the scour so formed near staggered piers was found maximum and around tandem downstream pier was found minimum. It confirms the shifting of sediment load away from this pier group and is deposited downstream, drifting more towards the staggered pier that is towards channel sidewall. Equations are proposed with respect to the pier spacing between tandem piers to evaluate the scour depth around individual pier of the pier group combination. Keywords Pier · Inline pier · Eccentric pier · Scouring depth · Scouring volume List of Symbols a s Scouring hole surface area for three pier’s group at equilibrium (m 2 ) a ss Scouring hole surface area for one pier at equilibrium (m 2 ) A Y intercept b Pier diameter or width (m) b cf , b cr Characteristic widths of upstream tan- dem and downstream tandem piers, respectively (m) B Slope of the regression line d se Maximum depth for equilibrium scour- ing for middle eccentric pier (m) d sf Maximum depth for equilibrium scour- ing for tandem front pier (m) B Subhasish Das subhasish.das@jadavpuruniversity.in; subhasishju@gmail.com 1 School of Water Resources Engineering, Jadavpur University, Kolkata, West Bengal 700032, India d sr Maximum depth for equilibrium scour- ing for tandem rear pier (m) d ss Maximum depth for equilibrium scour- ing for one pier (m) d xx xx indicates three different piers: tandem front, eccentric middle and tandem rear piers d 16 16% thinner sand grain diameter (mm) d 50 Median sand grain diameter (mm) d 90 , d 84 90 and 84% thinner sand grain diameter, respectively (mm) e Centre-to-centre distance in between upstream tandem and middle eccentric piers (m), 3b g Gravity acceleration (m/s 2 ) g ′ Relative gravity [g ′ = g(ρ s − ρ)/ρ ] h Approach depth (m) K sf , K sr Shape co-efficient of upstream tandem and downstream tandem piers b e Effective widths of pier (m) 123