Countermeasures for local scour around the bridge pier: a review

This paper aims to present the mechanism of scour and empirical equations for evaluating local scour with and without a countermeasure around the bridge pier. A critical review of scour countermeasures, mainly hydraulic, structural, and biotechnical, extending to the present time is done. Hydraulic countermeasures consist of river training structures and bed armoring. Structures placed parallel, perpendicular, or at an angle to the flow aiming to modify it is the purpose of river training works. Armoring is done through the use of riprap, partially grouted riprap, cable-tied blocks, grout-filled containers, and gabions. Structural countermeasures include foundation strengthening and pier geometry modifications. Extending footings, underpinning, and pile- underpinning are related to foundation strengthening, while pier geometry modifications include different pier features such as shapes, textures, slots, and collars. Biotechnical countermeasures include using vegetation riprap, geosynthetic polymer, live staking, and bio-stabilization using extracellular polymeric substances. Different combinations of countermeasures are also discussed. In hydraulic and structural countermeasures, riprap and collars are most commonly used due to their efficiency in scour reduction and economic feasibility. Bio-stabilization using extracellular polymeric substances is a novel measure for scour prevention. From the literature, it is concluded that pier modifications are the most effective and active area of research in which lenticular pier shape, lenticular hooked, and airfoil-shaped collar are best suited for reducing the local scour around the pier. Finally, the limitations of the countermeasures mentioned above are presented.