Prediction of scour depth and dune morphology around circular bridge piers in seepage affected alluvial channels

In alluvial rivers bridge piers often cause local scour, a complex phenomenon as a result of the interaction between turbulent flow and bed material. In this paper, the results of an experimental study on the scour hole characteristics around single vertical pier sets on a non-uniform sand bed, under no seepage, and with downward seepage conditions, are described. In case of downward seepage, turbulent statistics, such as Reynolds stress, higher order moments, TKE-flux, and consequently sediment transport, decrease upstream of the pier, while increasing on both sides of it, where the enhanced erosive capacity of the flow results in an increase in the scour hole width. Moreover, the scour hole length shifts downstream. Empirical equations for the evaluation of scour hole characteristics, such as the length, width, area, and volume, including the downward seepage parameter, are proposed and experimentally tested. Model predictions give reasonably good agreement with the experimental data.

Section: Experimental Facilitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Turbulent Flow Structures and Scour Hole Characteristics around Circular Bridge Piers over Non-Uniform Sand Bed Channels with Downward Seepage

Chavan¹,

Gualtieri

Kumar

2019

“…They found that the parameters imposing the dune morphology are the relative pier diameter, densimetric Froude number, wash-out parameter, and relative time. Chavan and Kumar [23] studied the features of dunes downstream of piers and found that the height of deposition increases with downward seepage. Pagliara and Carnacina [24][25][26][27] conducted a temporal analysis of dune morphology in the presence of debris accumulations at bridge pier in clear water condition and showed that the dune could be eroded under a given condition of high occlusion or high flow intensity.…”

Section: Introductionmentioning

confidence: 99%

Non-Intrusive Underwater Measurement of Local Scour Around a Bridge Pier

Poggi

Kudryavtseva

2019

A non-intrusive low-cost technique for monitoring the temporal and spatial evolution of the scour hole around bridge piers is presented. The setup for the application of the technique is simple, low-cost and non-intrusive. It couples a line laser source and commercial camera to get a fast and accurate measurement of the whole scour hole in the front and behind the bridge pier. A short campaign of measurements of the scour hole around a bridge pier in clear-water conditions is presented to provide a control test and to show how to apply the new method. Finally, the results are compared with two of the most used equations, for the time evolution of the maximum scour depth in clear-water conditions, to show the effectiveness of the proposed technique.

“…The upstream corner point (K M ) and upstream symmetry center point (K C ) were defined, too. To avoid the contraction effect, the pile width was designed for less than 10% of the flume width [19]. In the process of the experimental tests, the bed profiles in Figure 1c were measured.…”

mentioning

confidence: 99%

Comparisons of Local Scouring for Submerged Square and Circular Cross-Section Piles in Steady Currents

Liang

2019

The local scouring that occurs around submerged vertical piles in steady currents was studied experimentally in this paper. Three experiments were carried out for square cross-section (SC) piles and a circular cross-section (CC) pile with the same width. The key point scour depths, including the center of the upstream boundary point (K C ) and the two upstream corners (K M ), were observed over time. The two-dimensional profiles and the three-dimensional topography around each pile were measured using a Seatek. The different scouring characteristics of the SC and CC piles were investigated. The experiment results show that the scour depth at K C is much smaller than that of K M . The equilibrium scour depth of the CC pile is far less than that of the SC piles. The scour and deposition distributions were different between the CC and SC piles. The maximum scour depth was found at the lateral rear of the CC pile, and the maximum deposition was observed in sections of the SC piles. The evolutions of the scour depths at K M are predicted using a developed exponential equation.the scour depth will be independent from h c . By comparing the flow fields of h c /D = 0.5 and h c /D = 2.5, they found that the horseshoe vortex in front of the pile and the near-bed shear stress around the longer pile are stronger and wider in size, respectively. Moreover, there is an absence of vortex shedding for the shorter pile of h c /D = 0.5. For the square cross-section (SC) piles, Zhao et al. [13] observed that the scouring always starts at the two corners of the pile, and the bed level at the center of the upstream boundary remains almost unchanged before the scour pits extend there. Sarkar and Ratha [16] investigated the local scouring of non-uniform sediment beds around submerged CC and SC piles experimentally, but did not compare the different characteristics of the two pile shapes. Yao et al. [17] provided a relatively systematic report under live-bed scour conditions by carrying out a number of experiments. They found that the height-to-width ratio h c /D has a significant effect on the equilibrium scour depth and equilibrium time scale for the SC piles when h c /D is smaller than 4. Under their clear-water conditions, the Shields number was slightly smaller than the critical Shields number. The equilibrium time scale was found to reduce with an increase in the height-to-width ratio. Since the widths were not the same for the CC and SC piles, comparisons of the CC and SC piles were mainly conducted on the equilibrium time scale. Owing to the high flow intensity of the Shields number, the distributions of scouring and deposition for the two pile shapes did not show clear differences. Euler and Herget [18] stated that the size of the submerged piles and the approach flow velocity have significant effects on the scour hole shape and depth.Motivated by (i) the necessity of further research into the local scouring of submerged vertical piles, (ii) the significant effect of the flow intensity and pile height on local scouring, and (ii...