Live-bed local scour around vertical-wall abutments

Abstract

Local scour experiments were performed with four different uniform cohesionless sediment diameters d₅₀ = 0.26, 0.42, 1.06, and 1.92 mm and five vertical-wall abutments with projected lengths l = 0.04, 0.06, 0.08, 0.10, and 0.12 m perpendicular to the flow. These tests were conducted at different flow velocity (V) varying from 0.71 to 5 times of the critical velocity (V_c). The plotting of scour depths d_se vs. V/V_c shows that the scour depths increase up to the threshold value of flow (V/V_c = 1) and after that it reduces and again increases to attain the live-bed maximum in the flow range V/V_c = 3–5. It is observed that the scour depth increases with the increase of sediment sizes and abutment lengths. Further, the scour depth decreases with the increases of nonuniformity under all flow conditions. A design equation is proposed based on the present experimental data and existing live-bed scour data. The measured values of scour depth are compared with the calculated values using proposed equation and also with three different live-bed local scour equations for the conditions of the tests.

Keywords:

• scour
• bridge foundation
• abutments
• hydraulics
• rivers