Which term is used for protective rock placed around piers to guard against scour?

• A. Gabions
• B. Ballast
• C. Rip Rap
• D. Sag

Answer: (C)

Riprap refers to large, broken rock placed around bridge piers to shield the foundation from scour caused by flowing water. The loose, angular stones dissipate and deflect hydraulic energy, slowing erosion at the base of the piers and reducing the depth of scour holes. This protective layer is typically arranged around the pier footing and extends a short distance onto the riverbed, providing a durable barrier that resists movement under varying flow conditions.

Gabions are wire cages filled with rock used for erosion control and retaining structures, which can serve similar purposes in some contexts but describe a different installation method. Ballast denotes weight used to stabilize structures or components, not specifically a scour protection layer around piers. Sag isn’t a term used for protective rock surrounds in this context. Riprap best captures the protective rock around piers against scour.