3D jet and culvert scour

Abstract

3D full flowing horizontal jet scour has been traditionally used to simulate culvert scour in laboratory condition, while non-full flowing culvert scour has received less attention in the past. Current study focused on generalizing both horizontal 3D jet and culvert scour. Several experimental series were conducted and compilation of a database consisting of 738 jet and culvert scour datasets was carried out.

A thorough literature review was carried out and several research gaps in 3D horizontal jet scour phenomena were identified. The effect of relative tailwater depth, effect of relative sediment size, and effect of culvert shape remain areas worth exploring. Several series of experimental studies targeted at each research gap were conducted. Different sediment sizes and circular pipes of different diameter were used to study the relative sediment size effect. Different outlet submergence conditions revealed much about the detailed effect of relative tailwater depth. Observation of scour holes produced by different culvert shapes showed visual differences that were unable to be captured by the measurement of the maximum dimension of the scour hole or the conventional contour and centerline profile plots. The similarity and difference between different kinds of scour produced by full flowing circular jet and non-full flowing culvert under different hydraulic conditions are presented. Both the full flowing jet and the non-full flowing culvert scour were affected by the tailwater depth similarly. Culvert shape affected the jet flow pattern as the jet exiting from the culvert barrel, and this is the most obvious at very shallow tailwater depth condition.

A database consisting of 738 jet and culvert scour experiments was compiled and analyzed. The hydraulic radius (Rh) was found to be a suitable characteristic length scale across different culvert shapes for non-full flowing culvert scour. Analysis using the full database showed that Rh is the suitable characteristic length for both the full flowing jet and the non-full flowing culvert scour. The analysis included determination of a suitable representative sediment size for the 3D jet scour phenomena. For the maximum scour hole depth, the d84 is the representative sediment size, and the maximum scour hole width, length, and volume also have sediment size larger than d50 as representative sediment sizes. By using d84 = d50*σg to formulate a modified densimetric Froude number, Fo,d84, the non-dimensionalized maximum scour depth can be expressed as d as 𝑑𝑠𝑒/𝑅ℎ = 1.22𝐹𝑜,𝑑84.